In view of the difficulty caused by nonperiodic characteristic of frequency hopping sequence and the similar time and frequency characteristics to the general shortwave frequency hopping signal for detecting the differential frequency hopping (DFH) signal without parameters, an algorithm is proposed for detecting the DFH signal based on multi-hop autocorrelation. Utilizing different autocorrelation function distribution characteristics of DFH signal and noise signal, test statistics are established. The dwell-time and hop-rate of DFH signal are estimated with autocorrelation result. The test statistics are calculated with dwell-time. Utilizing the test statistics and hop-rate, the DFH signal is effectively detected. The result of simulation shows that the proposed method could effectively detect DFH signal with signal to noise ratio (SNR) larger than -18 dB. The performance of detecting differential frequency hopping signal under lower SNR could be enhanced by increasing data number.