Abstract: Several diagnostic systems used in implosion physics research were modeled by Geant4 toolkit, including the neutron imaging system, the filter-fluorescer spectrometer for hard X-ray diagnostic, the wedged-range filter spectrometer for proton diagnostic, the CVD diamond detector for neutron diagnostics, etc. The Geant4 simulation results were used to establish proper spectrum and images reconstructed algorithm, to optimize system design, and to estimate diagnostic system performance. Besides, based on the simulation, an experiment scheme was designed and calibration methods for the diagnostics were established.