Design of low-voltage, low-power CMOS Voltage-Controlled Oscillator(VCO) will be investigate in this thesis. We will discuss how to use transformer feedback to enhance transconductance to reduce power consumption and achieve high output swing at the same time. After using forward body bias, we improve the structure further. The differential VCO is implemented using TSMC 0.18um process. The EM simulation results with ADS momentum. A designed 10GHz VCO achieves a turning range of 9.5GHz, and phase noise about -112dBc at 1MHz offset frequency with power consumption 1.3 mW.