This paper proposed a wide-locking-range Divide-by-3 Injection-Locked Frequency Divider (ILFD3). In this paper, a fourth-order second harmonic enhanced resonator is proposed to strength the second harmonic and improve the mixing efficiency of the feedback signal and the injection signal. A new switched-capacitor tuning structure is also proposed. By setting sub-bands between every two operation bands, a wider locking range can be obtained without using much more switched capacitors. The locking condition based the fourth-order resonator is also analyzed theoretically in this paper. Fabricated in 28nm CMOS technology, the proposed ILFD can achieve locking-range of 22.5–30.4GHz (29.8%), and the total DC current of this circuit is 3.67mA with 0.9V supply.