Abstract: Fertilization was control instrument of productivity of cropland system ．Simulation of ten kinds of fertilization systems of rice cropping shows that the fertilizing progress can double the biomass and increase the paddy by 83％ ．N utrient in the system contributes 57．9％ of the output． the contributions of fertilizing are as follows：N is 20．4％ ，NP 30．8％ ．NK 32.8％ ．NPK 61．3％ and combination of organic and inorganic fertilizers 82.7％ respectively．Nature conductivity is 1／4 of the system conductivity or so．Petrochemical agriculture can maintain the conductivity in a period of time at the condition of nutrient balance and the conductivities of inorganic transform to organic and the nutrient inner circulation in the system have favorable output and the impact on system stabilization．The combination of organic-inorganic can not only improve the conductivity but also the potential conductivity of the fertilizing combination，the benefit of fertilization declines after some degrees of fertilization．Accompanying by fertilizing progress,improving the management is also important．