With the advent of Galileo and Chi- nese Compass, GNSS navigation technologies will develop rapidly. However, as the number of navigation satellites in view will increase, the fault probability will rise. This paper calculates the multi-fault risk of multi-constellation satellite navigation system in terms of MOPS. It is high- lighted that the probability of either one-fault or double- faults is higher than integrity requirement. The paper also describes a snap-shot ramose RAIM technology to protect civil aviation users in multiple-fault case. In this condition, a series of FDE calculation is adopted to separate satel- lites in sight into several groups. Therefore the problem will transform into several single-fault case, which current RAIM can solve. Simulation results verify that this tech- nique is proper to solve both single-fault and double-fault problem of civil aviation caused by application of multi- constellation GNSS.