Phase noise is a topic of theoretical and practical interest in electronic circuits, as well as in other fields, such as optics. In this work, a cross-coupled topology of integrated CMOS VCO design is considered. Based on Hajimiri’s phase noise model, we present the analytical model of phase noise in LC VCO. The calculation results are agreed with the experiment results. The model we presented can reflect the relationship between phase noise and circuit parameters. There is some instruction to VCO designer.