Abstract: HPGe detectors have a fine energy resolution, and are known as golden standards in nuclide analysis and considered as standard detective equipments in various detection areas. In the processing of HPGe detector, some parameters can be determined under Monte Carlo method. MCNP4 code is used to complete the simulation, and determined the material of entrance window and the thickness of the dead layer for coaxial HPGe detector, which based on the simulation result. Moreover, the code is used to compare influences of different materials and γ ray of different energy to the HPGe detector, then provide guidance for our future fabrication of HPGe detector. Furthermore, electric field simulation work inside the coaxial HPGe has been done, then the collection time of charges, produced from different energy deposition positions inside the coaxial HPGe, has been calculated. Changing positions of energy deposition can provide a perceptual intuition of the collection time of charges produced from different energy deposition positions inside the coaxial HPGe.