This paper proposes a new audio authenticity detection algorithm based on the max offset for cross correlation (MOCC) between the extracted ENF (Electric Network Frequency) signal and the reference signal. We first extract the ENF signal from a query audio signal. And then we partition it into overlapping blocks for forgery detection. The MOCC between the extracted ENF and the reference signal is calculated block by block. We also introduce an enhancement scheme to improve the quality of the ENF signal before the calculation of the MOCC. Our proposed method can detect not only audio forgery but also the edited region and audio forgery type. The effectiveness of our method has been verified by experiments on digitally edited audio signals.