During the aircraft flight test， maintenance activities are one of the main factors leading to aircraft unavailability. Currently， scheduled maintenance still accounts for a large proportion of preventive maintenance activities. Therefore， conducting research on maintenance interval optimization methods is of great significance for not only improving the quality and efficiency， reducing risks of flight test， but also guiding maintenance work. By comparing the differences between flight test and civil aircraft operations， a maintenance interval optimization method including steps such as data collection and preprocessing for a series of aircraft models， data fusion， modeling and verification， and determination of maintenance interval is constructed. Based on flight test data， the correctness and engineering applicability of this method are demonstrated， providing methodological support for maintenance interval optimization.