The laser scanner acquires surface information of a target by integrating laser ranging with the deflection angles of scanning components, making it suitable for applications such as topographic mapping and surface inspection. The laser projector achieves projection images by rapidly deflecting the scanning device to move the laser across the projection surface. It can be utilized in areas such as component installation, defect location, and more. In certain application scenarios, both laser scanning and laser projection are often used simultaneously. When employing separate scanners and projectors in coordination, a coordinate transformation is required between laser scanning and laser projection. The involved calibration process is both complex and challenging, thus significantly affecting work efficiency. The integrated scanning and projection system with a shared optical path avoids this problem. As a result, research on combining laser scanning measurement and laser scanning projection has gained increasing importance.The optical system presented in this paper consists of two liquid lenses and two sets of Galilean beam expanding structures. It features a two-stage beam expanding design, comprising a first-stage variable beam expanding subsystem and a second-stage constant beam expanding subsystem. The optical system achieves zoom functionality without any mechanical structures. To simplify the design process, two sets of compensating lenses are placed between the two liquid lenses. The first set of compensating lenses is concave lenses, and the second set is convex lenses. The two compensating lenses constitute a Galilean beam expanding structure. Since the common optical path system needs to consider the use requirements of two wavelength bands, it is difficult to correct aberrations well with a single lens. Considering that the cemented surface of the double-cemented lens may be damaged by laser, the positive lens in the beam expanding structure is replaced with a double-separated lens, which not only improves the degree of freedom to correct aberrations but also reduces the impact of spectral width on the system. Due to the limitation of the aperture of the liquid lens, the beam expansion ratio does not meet the requirements. To address this, a Galilean fixed-ratio beam expander with a beam expansion ratio of 1.5 is incorporated after the variable-ratio beam expansion structure, forming a two-stage beam expansion structure that further enhances the beam expansion ratio of the overall emission optical system. Using the Multi-Configuration Editor in ZEMAX, parameter settings are configured and simultaneously optimized for three configurations with different beam expansion ratios in the scanning state, as well as four configurations with different projection distances in the projection state.Under the scanning state, when the beam expansion ratios of the transmitting optical system are 3, 3.75, and 4.5, the divergence angles at the diffraction limit are 0.082 mrad, 0.066 mrad, and 0.055 mrad, respectively (Fig.7). This ensures that the optical system's performance meets the required standard of the divergence angle less than 0.75 mrad. According to the requirements of the Rayleigh criterion, the peak-to-valley value should be less than 0.25. The peak-to-valley values for beam expansion ratios of 3, 3.75, and 4.5 are 0.0129, 0.0472, and 0.133, respectively, all of which satisfy the criterion (Fig.8). Under the projection state, according to the spot diagram, the optical system has reached the diffraction limit at the focus positions of 5 m, 10 m, 20 m, and 30 m (Fig.9). The cross-sectional irradiance distribution diagram is obtained through simulation analysis using the physical propagation function in ZEMAX. The laser spot diameter is defined as the width between two points where the spot power density decreases to 13.5% of the maximum power density. Under the projection state, the spot sizes of the 520 nm laser and the 638 nm laser are 0.29 mm and 0.34 mm respectively at a distance of 5 m, 0.58 mm and 0.66 mm respectively at 10 m, 1.18 mm and 1.31 mm respectively at 20 m, and 1.76 mm and 1.95 mm respectively at 30 m (Fig.10, Fig.11). This meets the design requirements of the optical system, which are a spot diameter less than 1 mm within the range of 5 to 10 m, less than 2 mm within the range of 10 to 20 m, and less than 3 mm within the range of 20 to 30 m.The design results indicate that the design of emission optical system with common optical path for projection and scanning based on liquid lens is feasible. This design uses liquid lens instead of the traditional mechanical motion structure to achieve zoom, thus reducing the complexity of the system. By adjusting the liquid lenses, the optical system can switch between states for scanning and projection. The total length of the designed optical system is only 131.6 mm. This design offers a promising prospect in enhancing operational convenience, integration, and miniaturization.