With the development of the dual-frequency and multi-constellation global navigation satellite system(GNSS), the advanced receiver autonomy integrity monitoring(ARAIM) is proposed for providing global precision approach vertical guidance services. Based on particle swarm optimization(PSO) algorithm, the integrity risk allocation method is proposed. This method uses different allocation strategies for different particles in the algorithm, and selects the weighted sum of the vertical protection levels corresponding to different fault subsets as the fitness function. Each particle updates its own position and speed based on the principle of PSO algorithm. The algorithm is verified through real raw data of BDS/GPS navigation system and compared with the traditional method. The results show that based on the PSO algorithm, the vertical protection level is optimized and the ARAIM availability is improved.