For the problem of determination of maintenance time in demonstration phase of materiel, analysis method based on maintenance concept and maintenance function is put forward. Maintenance concept gives the constraints for maintenance time By analysis of maintenance function, the relation between a function system of materiel and a maintenance level, and the relations of maintenance actions of levels are clarified. To describe determination of maintenance time for convenience, taking example for intermediate-level maintenance, on the basis of the given maintenance concept, models of maintenance time are built, and flow-processes of maintenance function are given. According to above analysis result, mean maintenance time of intermediate-level is determined. It provides an important basis for trading off the relation of impacting among maintenance concept, maintainability requirement, and design of materiel.