Abstract: Light migration in nondestructive detection of farm products by using near infrared spectroscopy was little investigated, the theory based on the radiative transfer equation, and several models of this theory and the Monte Carlo method were described in this paper. Moreover, the applicability of these models was also analyzed. Based on known tissue optical parameters, the relations between the detection depth and measuring distance, thickness of overlying tissue were discussed by using Monte Carlo. It showed that the radiative transfer equation and Monte Carlo method was very useful in the field of nondestructive detection of farm product.