The measurement of microwave signals is of great significance because microwave signals carry important information in electronic warfare. However, conventional electronic microwave measurement systems are not suitable for transient frequency measurements of high-speed signals. A microwave frequency measurement technique is proposed and demonstrated based on frequency-power mapping. In this scheme, two optical carriers enter the phase modulator (PM) separately for phase modulation. The modulated signals are transmitted to a photodetector through a single-mode fiber. Besides, microwave frequency can be estimated by measuring the microwave power. This scheme avoids the bias drift problem of the intensity modulator and makes the system more stable. Therefore, this scheme is a promising IFM method. In addition, it is vital for its application in electronic warfare and high-resolution sensor systems.