Abstract: GEANT is an important Monte Carlo program and this program is in principal applied in high energetic physics. As the scale and complexity of high energy physics experiments increase, simulation studies require more and more care and become essential to the design and optimizing of the detectors, development and test of the reconstruction and analysis of programs, also to interpreting the experimental data. It has been found today applications also outside this domain in areas such as medical and biological sciences, radio-protection. With the development of space technique, design of the particle detector is helped by the Monte Carlo simulation too. The principal applications of GEANT in space particle detection are:the transport of particles through a detector for the simulation of detector response; the graphical representation of the setup and of the particle trajectories. GEANT uses the memory manager ZEBRA, it can help us to manage and store the data easily. In this paper, the primary structure and the process of particle transferring in detector is introduced. With GEANT program, many problems in particle detections can be solved, such as the particle's energy deposition in detector, the linear energy transfer in matter.