Monte-Carlo simulationsfor research on the influence of the inhomogeneous object in the medium on timecharacteristics of ultrashort pulse light propagation are presented. In frequency domain,the inflence of the position and size on imaging is analyzed by use of the difference ofamplitude or phase. The results show that the detection by the phase difference is moresensitive than that by the amplitude difference, and the higher frequency of detection,the more sensitivity of imaging. The geometric structure of light source and object hasthe influence on the imaging, the collinear structure has the best imaging effectiveness,the influence on imaging from changes of lateral position of the object is more seriousthan from changes of the longitudinal position of the object. The size of the object alsoinfluences imaging, the larger size, the better imaging. The resolution of imaging systemis determined by many factors, such as the SNR of detection, the geometric structure andthe optical properties of the object and so on.