The National Natural Science Foundation is a fund managed by the National Science Foundation. The National Natural Science Foundation of the United States covers about 1 700 universities and research institutions in 50 states of the United States, and receives about 40,000 research applications every year, of which nearly 1 000 projects are funded. In addition to about 5% administrative expenses and 3% entrusted projects, more than 90% of the funds of the National Natural Science Foundation of the United States are funded based on the merit-based evaluation of application quality. The project management of the National Science Foundation of the United States is based on the principles of "bottom-up" and "hierarchical evaluation" of project application. The project is collected from the whole country twice a year. After the scientists' research group submits the application, it will be reviewed and approved through peer review letters and expert review meetings. The fund includes a certain proportion of international cooperation and exchange funds.