As it can not get the dynamic behavior of PLL when using the traditional phase noise analysis method，the method of linear superposition is proposed to analyze the dynamic behavior of PLLs phase noise.Firstly，the phase noise model of each module of PLL is theoretically analyzed，and the contribution of the phase noise of each module to the total phase noise of the output clock is given.Then，the PLL device LMK04806 is taken as an example，the PLL simulation software is used to illustrate the influence of the parameters of PLL on the total phase noise by simulation data.Finally，a case is used to show that this method is of guiding significance for PLL design.