Based on the Semi-Markov mathematical description, the multiple states of maintenance processes for aviation weapon equipment are studied. Six kinds of maintenance states are determined and the Semi-Markov model of the maintenance process is given. According to maintenance characteristic, the multiple states maintenance processes are divided into the wait, use and alternate stages. Through using the mathematical model for the different stages, the probability in different states and effective index on different stages are obtained. These results are available to the maintenance practice. Based on the Semi-Markov mathematical description, the multiple states of maintenance processes for aviation weapon equipment are studied. Six kinds of maintenance states are determined and the Semi-Markov model of the maintenance process is given. Through using the mathematical model for the different stages, the probability in different states and effective index on different stages are obtained. These results are available to the maintenance stages.