An intravascular optical coherence tomographic (IV-OCT) system is developed, in which the diameter at the tip of the catheter probe is only 1 mm. In order to ensure the central axes of the Grin lens and the right angle prism attached to the micro motor shaft are aligned, a size-matching plastic sheath is designed to wrap the Grin lens. Then the Grin lens with the plastic sheath and the right angle prism are installed into a polytetrafluoroethylene (PTFE) sheath to assemble the probe, which has 1 mm diameter at the tip. A hardware filter is applied to removing the direct current component and the harmonic component in the k-clock signal generated by the swept laser source, and the resolution of the system is improved. The filtered k-clock signal is used as a trigger signal to resample the interference signal in the uniform k-space. Windowing, Fast Fourier Transform (FFT), logarithm, and background removal are applied to the resampled signal to get the A-scan data. At last, the coordinate transformation is applied to the A-scan data to reconstruct the circular display sample image. The axial resolution and the lateral resolution are 11.8 μm and 24 μm, respectively in actual measurement. The system imaging frame rate is 30 frame/s. With the proposed IV-OCT system, images of tubular white tape sample, shallot leaf, lotus root, and in vitro duck blood vessels are obtained.