Abstract: Sustainable land use and management is becoming an important research aspect in China and abroad,and the response of land productivity to changes of land quality is one of the core studies. In this study,the authors construct the model of marginal productivity of cultivated land with the changes of land quality in China by the method of function of production in economics. The method of function of production is usually applied in calculating the change of quantity of cultivated lands to contribution of marginal gross productions of agriculture. The authors use this method in measuring marginal productivity of cultivated land with changes of land quality. The model is as follows: lnY=a₀+a₁lnL+a₂lnF+a₃lnQ+a₄lnI+a₅Z+a₆T+Σb_iD_i, where Y is the productivity of cultivated land(kg/ha); L is the factor of agricultural labors per hectare(men/ha); F is the factor of chemical fertilizers per hectare(kg/ha); Q is the factor of land quality which is indicated by soil organic matter of cultivated land(g/kg); I is the factor of irrigation ratio(%); Z is the factor of disaster ratio of the disaster lands to all lands(%); T is the factor of time that represents technology developing; D is the fictitious variables of provinces. According to the model, we devise three projects and get the calculated results using the data of 30 provinces from 1981 to 1990. The results are satisfying and show that the main impact factors on productivity are chemical fertilizers,land quality and irrigation ratio in China. It is emphasized that the coefficient of output elasticity of land quality represent the influence of change of soil organic matter to marginal productivity of cultivated land. The coefficient is 0.257 in the average condition in the whde country, and is 0.425 in the provinces with low soil organic matter,and is 0.154 in the provinces with high soil organic matter. The coefficient represents that if soil organic matter increase 1%,the productivity of land will increase 0.257%, on an average, in the whole country,increase 0.425% in the provinces with low soil organic matter,and increase 0.154% in the provinces with high soil organic matter. Based on the study,the authors come to the main conclusions:(1)Improving the land quality is one of effective ways of increasing the productivity of cultivated land in China,especially in some provinces with low soil organic matter.(2)It is not best indicator to use soil organic matter represent land quality,so this maybe affect precision of the results. This question need to be studied deeply.