Abstract: The simulation system of cosmic ray muons detecting high-Z materials was established using Geant4 program. The relationship between the imaging results and the resolutions of position sensitive drift tube, and the imaging time of the system was studied using maximum likelihood algorithm. The results show that isolated high-Z materials can be rapidly identified when the resolution of the drift tube is less than 200 μm in 1-2 min. The study provides a theory gist for design and manufacture of drift tube.