Abstract: As one of the key parameters affecting the performance indexes of the radar receiving system, noise figure is closely related to the radar detection range. With the theory of equivalent conversion of a multi-port network model into a two-port network model, noise characteristic and gain of the phased array radar receiving system is analyzed and measured. Firstly, the equivalent gain of the multi-port network is computed by the equivalent theory. Then, based on the original definition of the noise figure, the formula of noise figure is deduced. At the same time, based on the equivalent theory, a direct measurement method of the noise and gain is presented. Finally, the method of computing and measuring noise figure and gain is verified by simulation and experiment.