Abstract: The maturity and color of fruits and vegetables influence their storage, transport and market effects.These are closely related to the economic benefits of these products.The characteristics of the delayed light emission (DLE) which is emitted from green plants several seconds after excitation can be used to evalute and grade fruits and vegetables according to their maturity and color nondestructively. In this paper , the fundamental characteristics of DLE, the mechanism of emission, the experimental apparatus and the method of measurement are presented. The paper also give the evaluation and grading of banana and orange with DLE as examples. The advantages of this method are wide adaptability, fast measurement, common light source and detector, high precision and suitable for mechanization.