This paper comes up with a cost rate function (CRF) aimed at the problem of hidden function system maintenance interval optimization of civil aircraft，and studs to propose the optimal preventive maintenance policy model and solution in “Overhaul period” based on Weibull distribution, which finally achieves the best optimization objectives of the maintenance task intervals of hidden failures (nonsafety effects) of civil aircraft system. Finally, the paper delivers the practical research by the reliability data of filter indicator pops of hydraulic system on B737, and proves the effectiveness and applicability of the optimization model and solution.