Based on the inter-relations between resources system, environment and ecosystem potential economic values under the frame of marine ecosystem, a marine ecosystem nonlinear system dynamics model is established in this paper. Then the marine ecosystem is simulated by the use of MATLAB software at a certain region, which indicates that the marine ecosystem serves the function of self decontamination towards the influence of light-level contamination of plastic debris to maintain a stable state, and that when the rates of resources exploitation or the rates of plastic debris into the ecosystem from the external environment belong to a reasonable interval which can be calculated by the model mentioned above, the marine plastic debris concentration would be stable and achieve dynamic balance; on the contrary, if the parameters exceed a certain value, and if no measures are taken, the marine plastic debris concentration would increase dramatically, the marine ecology resources would become exhausted, and the ecosystem would lose its potential economic value. Finally, a pre-warning mechanism for the marine ecosystem is set up and some suggestions are given in order to help researchers and ultimately government policy makers to understand the severity and potential global impact of the situation.