Nitrate leaching in farming soil is the main reason resulting in ground water pollution of nitrate. The main factors, which can affect nitrate accumulation and leaching greatly, include fertilization, precipitation, irrigation, soil characteristics, and cultivation system. Superfluous nitrogen in soil caused either by using chemical fertilizer and manure solely or compost will result in nitrate accumulation. Cultivation and plow systems also can affect the process of nitrate accumulating and leaching. Down flows due to irrigation or precipitation are the necessary condition and carrier for transference and leaching of accumulated nitrate in soil. Great pores are the main channels for down flows. These factors always work corporately. Mathematical model, which has been developed quickly and used widely, may be a good method to study and predict nitrate leaching in farming land.