Power is one of the basic parameters of microwave signal. Traditional power measurement methods are difficult to adapt to distributed long-distance network applications due tohigh transmission loss and large volume of coaxial cables. In this paper, a method of microwave power measurement based on electro-optic conversion is proposed. The microwave power measurement is converted to the measurement of modulation sideband rejection ratio. The relationship between microwave power and optical sideband rejection ratio is analyzed respectively forelectro-optic conversion methods using phase modulation and intensity modulation. Finally, the measured value is compared with the theoretical value. After electro-optic conversion, it can use optical fiber to transmit signals and carry out long-distance testing, which has a great application prospect in distributed long-distance networking.