With the rapid growth of the production and consumption of plastics, the waste and pollution of plastics become increasingly more serious. It is important to study the metabolic process of plastic resources to save the resources and protect the environment. Based on the material flow analysis method, a material flow analysis dynamic model of plastics was constructed in this study to analyze the life-cycle metabolic process of plastics from production, use, to waste from 1949 to 2018 in China. The flows and stocks of PE, PP, PS, PVC, ABS, PET and other plastic in 11 application areas were calculated, and the key points of resources waste of different kinds of plastics were analyzed. The results show that: (1) From 1949 to 2018, the consumption of plastics was 2205.6 million tons, and the output of waste plastics was 1404.8 million tons, of which 30.0% was recycled, 14.0% was incinerated, 36.0% was into landfill, and 20.0% was directly lost into the environment without treatment; (2) The in-use stocks of plastics were 630.0 million tons, and the loss stocks of plastics were 870.2 million tons, of which 66.7% were in landfill and 33.3% were carelessly discarded in the environment; (3) In 2018, the consumption of plastics was 193.1 million tons, and the output of waste plastics was 140.5 million tons, of which 32.0% was recycled, 26.0% was incinerated, 35.4% was into landfill, and 6.6% was directly lost into the environment. The study found that: The scale of plastic metabolism was large in China, and disposable plastic products had a great influence on plastic metabolism. Waste plastic was the key point of the resource loss, so the recycling of waste plastics was necessary. It was important to control the pollution of waste plastics that had entered the environment. Therefore in the future, research should focus on the risk and pollution mechanism of plastic waste scattered in the environment and improving the utilization efficiency of recycling and reusing of plastic waste, so as to reduce the loss of plastic resources and decrease the environmental pollution.