For the degradation problem of microwave signal phase noise caused by the additional phase noise of analog microwave photonic link, the characteristics of the white noise and frequency noise of microwave photonic link (MPL) were fully analyzed. The addictive phase noise (APN) model of MPL was established to expound the APN behaviors, and the correctness of the model was also verified by experiments. As for the typical applications of local oscillator optical distribution system, the EDFA-assisted MPL can be used to improve the APN. Experimental results indicate that the proposed phase noise model can be effectively applied to the microwave photonic link and can provide theoretical basis for the analysis and optimization of additional phase noise.