Abstract: Taking cracking and seating the existing cement concrete pavement with impact compaction technology on rehabilitation project as an example, the stress and deformation characteristics of the existing pavement structures and their soil subgrade in the process of impact compaction are studied using the three dimensional finite element method. Different locations of impact load on the pavement slab in the process are simulated and their mechanical behaviors for cracking and seating the slab and for compacting the soil subgrade are revealed. The relationships between the stress caused by impact load and the depth in soil subgrade are discussed. The scope of depth affected by impact load is proposed. The results obtained in this paper are helpful to the impact compaction practice on site and to the study on the mechanism of cracking and seating brought with impact compaction.