Quantum cascade lasers (QCLs) have important research and application value due to their ability to directly output lasers from mid-infrared to terahertz ranges. In this paper, the design and fabrication of QCLs are studied, with a focus on the etching method of ridge waveguide. For the waveguide composed of InP cladding layer and InGaAs/InAlAs active layer, a method combining dry etching, selective wet etching and non-selective wet etching is proposed to obtain ridge structure with little side erosion as well as vertical and smooth sidewall. Based on this etching method, a QCL emitting at 8.4 μm is prepared. Under pulsed operation mode at room temperature, a peak power of 10 W is achieved, with a maximum wall plug efficiency of 21.1%, which is at the leading level among long-wave infrared QCLs reported at home and abroad. An average power of 117.6 mW is obtained by increasing the duty cycle. This study has guiding significance for improving the design and fabrication of QCLs and optimizing the output performance of laser.