Abstract: The external friction behavior between the interface and the powder is affected by such factors as the properties of the powder, surface roughness of the die, the relative motion speed, temperature and pressure, etc. Unreasonable external friction behavior is easy to cause the wear of powder processing equipment and uneven distribution of product density. In order to explore the external friction behavior of powder, the research progress of powder external friction coefficient was thoroughly investigated, and the testing methods of powder external friction coefficient were summarized. According to different loads, the testing methods of powder external friction coefficient are divided into two categories: small load testing method and heavy load testing method. Among them, the testing methods of small load external friction coefficient include slope method and plate method, and the testing methods of heavy load external friction coefficient include rotation method, shear method and closed mold method. Following the above classification methods, the principle, testing equipment and important conclusions of various testing methods are briefly described. The results show that the test methods under small load are only suitable for measuring the external friction coefficient of low-density powder, and the pressing force in the test is generally less than 100 times of powder weight, while the test methods under heavy load are more commonly used for measuring the external friction coefficient of high-density powder. The pressing force in the test varies from material to material, and the pressing force of polymer materials is usually between 500 and 10,000 times of powder weight, while that of metal materials is between 10,000 and 1 million times of powder weight. Our team used the closed mold method to study the relationship between the external friction coefficient of the powder and the performance of the material under small load, and made some achievements. The closed mold method is a useful attempt to measure the external friction coefficient under small load.