The present invention relates to a method for predicting the reliability of an aircraft system (S) onboard an aircraft, constituted by a plurality of elements. The operation of the aircraft is constituted by a sequence of cycles, each cycle comprising a flight phase and a ground station phase. The method of reliability prediction allows in particular calculation of the breakdown probability of the aircraft system at each cycle of operation of the aircraft. The present invention can also estimate the rate of operational interruption of this system.