Abstract: The parameters of coated fuel particles are important to the safety operation of high temperature gas-cooled reactor. The density of porous pyrocarbon layer is one of the important parameters of coated fuel particles, which directly affects the performance of coated fuel particle and fuel element. A measurement method for the density of porous pyrocarbon layer was introduced in this paper. By this method, the density of coated layer was calculated by particle size and individual weight of particles before and after coating. The particle size and individual weight of particles were measured by particle size analyzer and balance. The accuracy of this method was researched. The results show that the accuracy can satisfy the test requirement. And this method is very efficient for engineering application.