Abstract: A method to measure the density of rock fill by use of the rigidity correlation method is put forward with regard to the characteristics of the rockfill of Yanshan Reservoir. The rigidity (K), the vibration mass (m) and the density ( ) at the same site are measured according to different rock properties, gradations and densities. A linear relation equation between the rockfill density of Yanshan Reservoir and the normalized dynamic rigidity of additive based on the rigidity correlation method is established. The test results show that the rigidity correlation method used to check the density of rockfill in Yanshan Reservoir is proper, and that the density test error satisfies the design requirements by calculating relevant modulus and error analysis.