As an emerging coherent detection technology, terahertz time domain spectroscopy (THz-TDS) technology has promoted the progress and innovation of safety testing and nondestructive testing technologies, and has made outstanding contributions to the protection of people's life and health and property safety. In order to obtain better imaging results and detection sensitivity, it is necessary to increase the detection speed of terahertz signals while ensuring that the signal-to-noise ratio of the acquired signal meets the requirements. Based on the involute reflector optical delay line device, this paper analyzes the optical delay line shape parameters, and simulates a model with a delay distance of 71 mm and a delay time of 236.7 ps. The error analysis is made in three aspects: the eccentric error of the axis of the rotating mirror, the installation error of the planar mirror, and the outgoing spot distortion of the rotating optical delay line, and the method of reducing the error is discussed. It provides a theoretical and simulation basis for the device to increase the time delay, obtain a more complete terahertz spectrum, and further improve the performance of the THz-TDS system.