Based on the elastic layered theory system, the vertical additional stress distribution along the depth direction of subgrade under different driving loads of full depth asphalt structure and ordinary semi-rigid base asphalt pavement structure were analyzed in this paper. The influence of axle load level, subgrade modulus and other factors on the subgrade service depth were analyzed quantitatively. The research results show that the thicker the pavement structure thickness is, the smaller the subgrade service depth is, and the two have a linear relationship. The subgrade service depth of full depth asphalt pavement is much larger than that of semi-rigid base pavement. With the increase of axle load, the depth of subgrade working area increases gradually, and the relationship between them is approximately linear. For different pavement structures, appropriate subgrade working areas should be set according to the thickness of the pavement and the traffic conditions. The depth of subgrade working area increases obviously with the increase of subgrade modulus, and the relationship satisfies quartic polynomial. Subgrade modulus is the main factor affecting the subgrade service depth.