Abstract: The gap-graded coarse-grained soils are commonly encountered in geoengineering applications. However, their compaction characteristics remain unclear. By conducting a series of compaction tests, several influencing factors are studied. The test results show that compared with those with continuous gradation, the coarse-grained soils without grains sizing below d₃₀ are less compactible, while the absence of grains sizing between d₃₀ to d₆₀ will increase their compactibility. The dry density of the gap-graded coarse-grained soils increases with the increase of the fractal dimension D of basic gradations, and the dry density reaches the maximum value when D=2.5~2.7. It is possible to achieve the largest dry density of the coarse-grained soils by selecting a reasonable mass content of fine-grained group. The optimal mass content of fine-grained group is related to the dry density of conarse-grained group, the dry density of fine-grained group and the interference between coarse and fine grains during the process of packing. Based on the experimental results, a model aiming to predict the dry density of gap-graded coarse-grained soils is established. Using the prediction model, the relation curve between dry density and mass content of fine-grained group can be obtained through a few compaction tests, and the optimal mass content of fine-grained group and the applicable mass content range of fine-grained group can be calculated, which can greatly reduce the test workload.