Scanning speed is an important parameter of monitoring receiver, which is designed for radio monitoring. The magnitude of receivers’ scanning speed has improved from dozens MHz/s to hundreds GHz/s, due to the advances in technology. The current detecting method is very demanding. Detecting method in this paper is to use two general signal generators, whose signals fall in the range of monitoring receiver. Then the intermediate frequency of receiver output to modulation domain analyzer. When the receiver receives the two CW signals, a modulation domain analyzer can measure the time interval of the receiver’s intermediate frequency. The ratio of frequency differences between signal sources and time interval is calculated, and consequently we can infer the receiver frequency sweep speed. This measure method can easily detect scanning speed whose order of magnitude is up to hundreds GHz/s, and has no special constraints to signal sources and the modulation domain analyzers.