Based on limited time intervals between missions, a mission reliability model is built for complicated equipment system. Aiming at enhancing of missionary reliability of equipment, minimal repair, preventive maintenance and corrective maintenance are taken as options for components of the equipment, and a selective maintenance decision-making model is constructed taking the maximization of reliability as the objective. An optimal decision-making measure based on the genetic algorithm is brought forward to solve the solution explosion problem. The case study shows that the decision-making model and the optimal solving measures are applicable.