An all-optical transmission switching model based on electron spin relaxation was designed, and this new configuration of optical switch grants the features of short switching time, simple structure, and high optical nonlinearities. The exciton saturation caused by phase-space filling (PSF) and Coulomb screening(CS) in GaAs/AlGaAs multiple quantum well was discussed under the right circularly polarized pump beam. The absorption coefficients variations of the circularly polarized probe beam in the same and opposite polarization direction with the pump beam were calculated. The differential transmission change of both polarization as a function of delay time was obtained. The pump-probe experiment was carried out to measure the change curve in transmission of the same circularly polarized states probe beam at room temperature, and obvious saturation phenomenon is observed which agrees with the numerical result.