Abstract: The present paper by the four districts of Lanzhou city aims at the degradation Law of several main pesticides in vegetables and studies the initial residual concentration of these pesticides setting up two different types of pesticides of drug forms for an evaluation method of polluted vegetables. The evaluation parameter consist of the four factors the initial residual concentration of pesticide; the degradation rate of pesticide; the interval period from the last applying pesticide to harvest; and the evaluation standard. In this paper, the pollution index PI₁ and PI₂ of vegetables express the pollution level that the different pesticides are applied to different vegetables to obtain some important results.