With an increasingly extensive application of overhead-cable mixed lines in the distribution network， a new fault line detecting method with correlation analysis using wavelet packets decomposition is proposed based on the features of big capacitance current of overhead-cable mixed lines as a single phase grounded fault occurs. By using the good frequency dividing characteristic of wavelet packets， the transient zero sequence current of each line is decomposed to obtain the outputs of different frequency bands after the occurrence of a single phase grounded fault in the distribution network. The characteristic wave band can be determined by the theory of maximum energy. According to the similarity weakest principle of the capacitance current between the fault line and faultless line in the characteristic wave band， the fault line can be detected by a correlation analysis of wavelet packets decomposition factors from the characteristic wave band. The theoretical analysis and simulations indicate that the fault line detecting method is correct and reliable for the distribution network with overhead-cable mixed lines.