This passage studies on theory and scene simulation of NLOS imaging. Based on math and physical properties, a simulation platform is built for a NLOS imaging system, including a femtosecond laser, a scanning galvo system, a lambertian surface, several hidden scenes, an ultrafast photodetector to transfer the intensity of laser echo signal to voltage value and a TCSPC module to produce intensity-time histograms. By the simulation platform on MATLAB, precise imaging of the scenes is accomplished. Results show that multi-path analysis using echo signal intensity versus time provides enough proof to reconstruct 3D geometry of a hidden scene. © 2017 SPIE.