Abstract: The relationship among the narrow-band envelopes correlation coefficient (Frequency-envelopes correlation) of ship noise, R, the mid-frequency difference △f_ni of filter, the initial filter mid-frequency f_n, the filter pass-band △f and the time-delay τ is presented. The relation curves mentioned above are compared with the R - △f_ni curve of sea ambient noise. It is shown that there exists significant difference between the frenquecy-envelopes correlations of ship noise and sea ambient noise.