Optical coherence tomography (OCT) is a high resolution imaging technology developed in the recent years and based on many cutting-edge sciences and techniques. The principle is introduced, the OCT system based on time linear modulation and Michelson interferometer is given with its initial experimental results. The optical spectra of the light source and uneven scanning speed of reference delay line are emphasized by the simulation and experimental research. Using the FFT method, the analysis of parameter properties based on experimental results and their influence on practical coherence tomography is presented from the point of view of engineering designing, therefore the improved method is obtained.