A novel frequency search algorithm is proposed in this paper to achieve fast locking in all digital PLL (ADPLL) with no phase tracking being required. According to phase and frequency error, the normalized tuning word (NTW) is calculated so that the output frequency reaches the desired frequency immediately. As the non-idealities, such as DCO gain estimation error and TDC finite resolution, greatly affect the accuracy of the calculation, the output frequency is continuously measured and frequency error is averaged to minimize those impacts. With 0.13um CMOS process, the proposed ADPLL operates at 2.7 GHz and achieves 0.35 us locking time while consuming 7.47mW.