With the rapid development of space technology, the requirement of power capacity for microwave component loading is higher. Meanwhile, the affection by the Multipactor effect is becoming more prominent. So, the establishment of effective Multipactor detection means is particularly important. In this context, we have developed a set of Multipactor monitoring system. In this system, the forward/reflected power detection method and the Nulling detection method are used to realize the Multipactor detection. This paper firstly introduces the mechanism and harm of Multipactor effect. Then, the idea of developing the system,the whole system design and Nulling detection principle are described in detail. Finally, the experimental results show that the system is able to realize the Multipactor effect detection of passive microwave components in single carrier state.