Capacity is an important indicator in communication systems performance, the capacity of Orthogonal Frequency Division Multiplexing/Offset Quadrature Amplitude Modulation(OFDM/OQAM) system over multipath Rayleigh-Fading channels is thoroughly investigated. Through analysing the probability density function(PDF) of Rayleigh channels model and deducing the alliance of probability density function in two random relevance Rayleigh channels, we get the mathematical expression about the mean and variance OFDM/OQAM system capacity in multipath Rayleigh-Fading channels, which the function of the parameter is related to the number of the subcarriers of an OFDM/OQAM system, the signal to noise ratio(SNR) and the number of multipath. Simulating the system, we analyse the influence of the mean and variance OFDM/OQAM system about the parameter. The result shows that the systems mean is proportional to SNR and inverse proportional to the number of the subcarriers; the systems variance is defined by SNR and the number of multipath.