Although most GNSS monitoring stations located in open and clear places,multipath effects by surrounding environment could not be avoided,which leads to severely degraded observations of GNSS monitoring stations.This paper proposed a multipath detecting method based on antenna arrays,benefiting from different arriving angles of the multipath signal and the satellite signal.This method firstly computes the arriving angle of the satellite signal based on prior information such as satellite ephemeris,the coordinateof the monitoring station,etc.Then the steering vector of the satellite signal is obtained referring to the relative position of the array element.We design the array weights according to the steering vector,so as to minimize the satellite signal power of the array output.Therefore,if there is multipath in the received signal,the correlation peak could be detected in the array output,otherwise could not be detected.So we connect the array output to a GNSS receiver.When the receiver gives out observations such as pseudo-ranges and carrier phases,we predicate multipath to be existed in the received signal.When the receiver is not able to capture the satellite signal,there is no multipath which could affect the observations.Simulations based on software receiver show that the proposed method is able to detect multipath in the received signal quickly and effectively.The results could be used either in evaluating the signal quality of the monitoring stations,or in eliminating the multipath.