The measurement of EIRP (Effective Isotropic Radiated Power) is an important test in satellite onorbit tests，which represents the quality of the communication link and receiving satellite data. The previous methods generally use the manual test, which is not only inefficient, but also has sometimes the low accuracy of test results. This paper provides an automated test method of EIRP, in which through a host computer to automatically collect the data and calculate EIRP. It avoids the artificial error of the traditional test method, which has the advantages of high efficiency and realtime. Taking the FY3C’s EIRP test as an example, the test procedures of the method are briefly described.