Abstract：Based on summarizing the existing matrix maximum eigenvalue method(MMEM) of RAIM availability evaluation, we improve the mathematical model in the existing RAIM availability method under double-satellite faults conditions, and propose the maxima method(MM) of RAIM availability evaluation. Based on the given integrity risk parameters and the BDS measured data of 8 tracking stations in China provided by the international GNSS monitoring and assessment system(IGMAS) on September 6, 2020, we use the two methods to calculate the horizontal protection level(HPL) under double-satellite faults conditions to compare and analyze the RAIM availability performance of BDS. The results show that the MMEM-based RAIM availability is lower than that of the MM in non-precision approach(NPA) in China, the overall MMEM-based RAIM availability is higher than that of MM, but the MM method consumes less calculation time. The MM-based RAIM availability can fully meet the route and ocean stages, and the MMEM-based RAIM availability can fully meet the terminal, route and ocean stages. The MM-based RAIM availability has rigorous theory, a simple mathematical model, and is easy to program. It is another RAIM availability evaluation method besides MMEM.