To further develop the optimization technology of alpha particle energy spectrum detection parameters based on Monte Carlo simulation method, this paper uses PyQt5 to design a software that calls Monte Carlo simulation package Geant4 for alpha particle energy spectrum simulation research. On the one hand, a physical model of the Passivated Implanted Planar Silicon detector for measuring α particles is established, and the simulated physical process, model materials, particle source geometry, composition and other parameters are corrected according to the actual α particle measurement conditions, combined with the PyQt5 interface. The development platform visualizes functions such as particle source parameters and detector parameter modification. The detection efficiency of the model is obtained by performing simulation experiments under multiple detection distances and different vacuum pressure conditions, and after the acquired energy is deposited into a spectrum, it is broadened by the EMG-Landau (Exponentially Modified Gaussian and Landau) response function model. On the other hand, to verify the accuracy of the detector model, the detection efficiency of the simulation results and the measured results are compared. The experimental results show that the detection efficiency errors of both are within 5%, and the EMG-Landau response function model broadened works well. The research results of this paper verify the reliability of the Geant4 simulation software in the study of α-particle energy spectrum. The software can directly modify the measurement conditions of α-particle energy spectrum, simplify the simulation steps, and improve the simulation efficiency, thus provides a powerful tool for α-particle energy spectrum detection parameter optimization technology.