Based on measured data of the Sutong Bridge's north main pier during operation period, the paper analyzest the axial force of pile body, and then evaluates the effect of bearing capacity of the pile group foundation on the riverbed protective layer. According to the monitoring data, both the axial force and its amplitude of variation weaken sharply after piles pass through the riverbed protective layer. It shows that the riverbed protective layer used by the Sutong Bridge is of great significance in improving bearing capacity and global stability of pile group foundation, controlling settlement and improving force transfer mechanism.