Schedule maintenance task interval is a key index representing the reliability and economy of an aircraft. Since the initial maintenance interval approved in Maintenance Review Board Report (MRBR), obtained by MSG-3 analysis method, is relatively conservative, it is significant to optimize the maintenance interval based on in-service data. This paper studied the work flow of the maintenance interval optimization. First, we give the equation to determine the sample size which must be satisfied to initiate the process. Then, we provide a failure trend fitting method which helps us to decide if it is necessary to do the job. Finally, we illustrate the hypothesis test criteria which tells us whether the new targeted interval should be accepted or rejected. The result shows that the proposed method can be used to determine if the new desired maintenance interval for a specific task can be accepted, which further leads the update of the MRBR.