In this study，we designed a voltage-controlled oscillator(VCO)with a low phase noise operating in the K-band based on the standard 65 nm CMOS process. The oscillator adopts a negative-resistance type LC structure； the negative-resistance unit is an all-NMOS structure that can increase the tuning bandwidth. We proposed a tail current source structure that can control the switch of the VCO and the magnitude of the tail current. The noise at the second harmonic is filtered out through the resonance of the inductance and the parasitic capacitance of the cross-coupled transistor，further optimizing the phase noise. The results indicate that under a supply voltage of 1. 1 V，the VCO achieves an output tuning frequency range of 18. 66 – 22. 17 GHz，with a minimum phase noise of . 109. 91 dBc/Hz at an offset of 1 MHz. The proposed design presents the advantages of low phase noise and wide tuning range.