Abstract: Objectives: The advanced receiver autonomous integrity monitoring (ARAIM) algorithm equally allocates the integrity and continuity risk, which leads to a conservative protection level (PL) calculation. Methods: This paper systematically analyses the factors affecting the protection level calculation, proposes an optimal risk allocation method for ARAIM considering the dilution of precision (DOP), and verifies the effectiveness of the method by using three kinds of data from the MGEX (multi-GNSS experiment) station, vehicle and airborne experiments. Results: The results show that the proposed method can realize a tighter envelope of the protection level to the position error, and its performance is better than that of the half-interval search method. Compared to the riskaveraged method, the PL improvement rates of BDS in the three types of experiments are 7.5%, 11.6% and 8.8%, respectively. In addition, the PL optimization effect is closely related to the satellite observation geometry, and the improvement effect varies within different systems and regions. Conclusions: For BDS, the improvement in the non-Asia-Pacific region is better than that in the AsiaPacific region, with 3.6 m and 1.0 m respectively in the two regions. In the Asia-Pacific region, the optimization effect in BDS and BDS/GPS is 1.0 m and 0.6 m, respectively, with the single BDS enhancement being more significant.