A new signal amplitude transmission model is presented with polarization mode coupling(PMC) effect in the optical fiber.The received signal amplitude of the long optical fiber was given,based on the multi stage matrix expression,while the effect of PMC is considered.The physical analysis of our model is supported by a number of practical tests.Results from the approximation calculation of BER to estimation the effect of polarization mode dispersion(PMD) and PMC has shown that system performance penalty is being worsen when the PMD is larger than the 10 % of the signal code period.