In the optical measurement of infrared smoke screen,considerable confusion exists regarding the applicability limits of the Lambert-Beer law of optical transmission.By means of the approximate Vander Hulst numeration method and random-walk particle-puff model(RPPM),the calculation of smoke transmission based on first-order multiple scattering approximation is improved on,and it is used to simulate an infrared smoke transmission test.Numerical simulation indicates that it is more accurate to receive the effective smoke transmission.