Abstract A mathematic model of solid attitude monitoring is worked out based on the generic formulating theory of solid attitude and reasonably approximate disposal. And a new way of output shaft alignment attitude real-time monitoring is excogitated for a marine main engine air mounting system. Then the way is analyzed and validated by simulated and testing results. The simulated results show that the error of the mathematic model of solid attitude monitoring is very small and can be ignored. The testing results show that this way has good capability in engineering use.