In order to solve the problem that continuous wave active sonar is easily exposed by the sonar array when detecting targets, an active non-linear frequency modulated continuous wave ranging method based on digital delay and resampling technology is proposed. The continuous wave measurement signal with non-linear frequency variation is generated by the signal generator. After the signal is returned by the measured object, it is mixed and filtered with the original signal to obtain the measurement mixing signal. According to the digital model of the original excitation signal, a reference signal with digital delay is constructed along the way. The reference signal and the echo signal are mixed and filtered to get the reference mixing signal. The reference mixing signal is used for zero-crossing resampling and spectrum analysis of the measured mixing signal, the main frequency of the signal is extracted and then the distance of the measured object is calculated. The underwater resampled nonlinear frequency-modulated continuous wave ranging experiment system is built. and according to the laboratory measurement results, the repeatable standard deviation is only 0.083 m and the average error is better than ±8.5%, which verifies the feasibility of the ranging method, the main sources of ranging errors are further analyzed. Through the comparison and simulation of the generalized cross-correlation time delay estimation algorithm, it is confirmed that the propagation time delay cannot be accurately estimated by using this method, and the safety of ranging is improved.