According to the fact that intelligent substation inspection cycle calculation is over-reliant on experience and lack of theoretical support, an calculation method of inspection cycle based on reliability analysis in intelligent substation is proposed. The method is discussed on an intelligent substation based on IEC 61850 with a breaker-and-a-half configuration. Firstly, the minimum cutting set of the equipment that causes the failure of the substation system is obtained through Fault Tree Analysis (FTA). Secondly, through the logical connection between the possible fault-point and the relevant equipments, combining with the original reliability data of various devices (availability, unavailability, failure rate) from the related literatures,the reliability data of possible fault-point is obtained.Thirdly, using the Analytic Hierarchy Process to obtain the weight relationships of three types of reliability data, the reliability of the possible fault-point is calculated after weighted calculation. Finally, through the function relationship between the task reliability and the inspection cycle, the inspection cycle of possible fault-point is obtained. Because this method converts the reliability data of various equipments into the reliability of possible fault-point, it can more effectively meet the actual needs of the cycle calculation and is of great significance in ensuring the safe and stable operation of intelligent substations.