The output signal-to-noise ratio （snr） of correlation detectors is analized.A correla-tion detector is a divice

which consists of two input filters

one output filter and one multiplier

and has two input pairs of terminals and one output pair of terminals.Unlike that described in papers[1][[2][[3] and[3]

effects of input filters are consid ered in this paper. The formulation concerning the relation between the input snr and the output snr are derived

and special working conditions of correlation detectors are discussed.The conclusion is us follows: For small snr

the output snr is proportional to the products of two input snr; if the input snr of one channel is much lorger than the other and than 1

the output snr will be proportional to the smaller input snr; for all conditions （either strong signal

or weak signal） . the output snr of correlation detectors is comparable to the squar law detector’s.