Oceans, from which people could gain marine biologic resources, are considered as one of six types of basic ecological productive land areas of Ecological Footprint Model proposed by William Rees & Mathis Wackernagel. As a result, it is safe to draw a conclusion that marine biologic resources are very important. Because marine biologic resources are typical renewable resources, the maximum sustainable yield of marine biologic resources will be accessible if rational empolder strategy is adopted. Based on the conceptions of ecological footprint and biocapacity, we put forward new conceptions of marine footprint and marine biocapacity. According to their nonlinear dynamic relationship, a quadratic nonlinear dynamic model for marine footprint and marine biocapacity in this paper. Moreover, the value of the model is calculated and the results are analyzed in terms of the theory of stability analysis. The results show that: (1) The marine biocapacity is positively correlated to its growth ratio and negatively correlated to marine footprint’s growth. (2) For the sake of the sustainable empolder of the marine biologic resources, the maximum growth ratio of marine footprint should not be overrun r/xm（r refers to marine biocapacity growth ratio, and xm refers to maximum marine biocapacity）. Only in this way, can the maximum sustainable marine footprint be equal to rmx/4, and the marine biocapacity will hold out steady equilibrium, the half of the maximum marine biocapacity.