Vehicle load is one of the most important factors influencing service performance and service life of pavement. In the pavement design and analysis, different axle loads need be conversed to the standard axle load based on the equivalent deterioration principle of pavement. Pavement surface deflection values under different axle loads have been measured on several expressways in this paper. The correlation relationships between deflection and axle loads are analyzed. The regularity of deflection and axle conversion index based on deflection equivalent are analyzed, too. The axle conversion formula based on deflection equivalent for asphalt pavement is regressed according to the actually measured deflection data. This research achievement can provide us with a reliable axle load conversion method for asphalt pavement design.