Due to the fact that coastal areas of China are characterized with a significant amount of silty fine sand with poor gradation, it can be used as roadbed filling materials for the reduction of the reliance on foreign soil. Based on a tourist highway progect in Hainan, a PFC2D model has been established for the compaction process of poorly graded fine sand subgrades, followed by a research on the compaction effects of compaction force, static and dynamic rolling, and compaction passes, thus building the relationship between compaction degree K and porosity n. The results show that the porosity of fine sand remains relatively consistent at different depths under varying rolling compaction forces. Compared to static rolling, dynamic rolling is characterized with better compaction effect and deeper action depth. As the number of rolling passes increases, the porosity of fine sand decreases while the compaction degree of the roadbed increases. However, after a certain number of rolling passes, the improvement in compaction effect becomes less significant. The numerical simulation results are consistent with the field test results.