Abstract: The P forms,quantity and cycle approaches in natural ecosystem are summarized, and its sources, quantity,input and output approaches under conventional and organic farming condition are compared.Utilization efficiency of P and influencing factors are also analyzed. The research indicates that in organic farming system,there exists negative P balance because the input of P is lower and the output of P is nearly the same as conventional farming system,but the using efficiency of P is higher than that of conventional farming system. This makes a great significance for the positive environmental effect of P.