Abstract: Based on the other scholars ' researches, and considering the similar ratio of sand, two groups of model tests are done under self-designed model piles and loading installations. The conclusion of load-displacement law, ultimate bearing capacity law, internal force of pile shaft and resistance of soil surrounding single pile are drawn under the action of combined load. The influence mechanism of horizontal loads on vertical bearing capacity and that of bending moments on horizontal bearing capacity are analyzed. Some improvements of pile shaft design under combined load are proposed.