The maximum density of coarse-grained material is the control index obtained after the scale of the prototype on the basis of the ingredients. There are obvious scale effects. In order to study the difference of relative density between the laboratory and field test of coarse-grained dams, the comparison between the laboratory test and field test was carried out for the same dam material using the equivalent replacement method, and the results indicated that in the process of rolling test, because the dam material particle size is bigger and easier to compact, and the compaction machinery, compaction energy and other aspects are different from laboratory tests, the maximum dry density obtained from field compaction test is bigger, whose maximum dry density was 2.35 g/cm3, and the maximum dry density was 2.31 g/cm3 for the laboratory test, which was 0.04 g/cm3 higher than that of field compaction test. The P5 content corresponding to the peak value of the maximum dry density in the field test was 80% and the P5 content corresponding to the peak value of the maximum dry density in the laboratory test was 70%.With the increase of the coarse aggregate size, the P5 content corresponding to the peak value of the maximum dry density increased.