At present, in the relevant design specifications for earth-rock fill dams in China, the filling standard of rockfill materials is expressed by porosity. Although the mechanical properties of coarse-grained soil are closely related to its porosity, the properties of coarse-grained soil with different gradations are not the same even if the porosity is the same. Porosity can’t express compactness, while relative density can represent compactness of coarse-grained soil. In order to control the deformation of dams reasonably, it is necessary to carry out the field relative density test of rockfill materials. In this paper, limestone rockfill is used to test. The results show that: (1) the bucket diameter of relative density tests has a certain influence on the maximum and minimum dry density of limestone rockfill. (2) In the range of test gradation lines, with the increase of the content of P 5, the maximum and minimum dry density all show the trend of increasing first and then decreasing. (3) When the content of P 5 is the same, the maximum and minimum dry density of limestone rockfill increase with the increase of the maximum particle size, and the particle size has a significant impact on the maximum and minimum dry density.