Based on the existing particle beam therapy, combined with the existing advanced technology in photon radiotherapy and the particle beam therapy system development platform, this project optimizes the existing radiotherapy scheme, and forms a multi-mode guided multi particle combined with biological intensity-modulated therapy technology. Based on the theoretical analysis and computer simulation, a high-precision three-dimensional Monte Carlo simulation model of complex magnetic field, multi particle beam and patient was established through the research of fast Monte Carlo simulation and validation method for MRI guided particle intensity modulated radiation therapy (IMRT). According to the IMRT plan provided by the radiotherapy planning system, the radiation source is modeled. The GPU accelerated Monte Carlo verification software and CPU / GPU heterogeneous parallel computing hardware are constructed. Through fault-tolerant processing and performance optimization of the software, the stability and speed of calculation are improved, and the fast Monte Carlo calculation is realized. The results were further verified by using mature commercial Monte Carlo software and particle radiotherapy Monte Carlo based on GPU accelerator. The Monte Carlo simulation and verification of magnetic resonance guided multi particle joint intensity modulation were carried out. The interaction of photons, electrons, protons, carbon ions and other multi particles in the human body under complex magnetic field environment was studied, and the interaction of multi particles in the heterogeneous medium in the patient's body under complex magnetic field environment was accurately simulated.