Abstract: The phase noise of Voltage Control Oscillator(VCO)is influence to the sensitivity in wireless radio frequency receivers. Therefore,we focus on researching the low phase noise design methods.In this work,based on Hajimiri phase noise model,we present the analytical model of phase noise in LC VCO.The model calculation results are agreed with that of experiment.The model we presented can reflect the relationship between phase noise and circuit parameters. There is some instruction to VCO designer.