Pile in karst areas often impales the caves with different height and often bears the vertical load on pile top or unilateral overload，but worst of all，the working mechanism of the pile impaling cave is not well under? stood. Due to this problem，the lever loading device was designed，the strain of pile when impaling the caves of different height with applied vertical load on the top of the pile was tested，the strain of pile body，the earth pressure and horizontal displacement under unilateral overload were tested when the top of the pile is free，and the transfer law of axial force and the response under unilateral overload of pile impaling the cave of different height were ob? tained. The results show that：1）When the vertical load is applied on the top of the pile bears，before the pile enters the rock layer from the soil layer or the cave，the axial force-depth curve is of obvious interface effect，that is the pile′s axial force at the bottom of the soil layer or the cave grows，and the growth rate increases with the increase of load. The axial force-depth curve of the cave is "concave"，its magnitude of the concave increases with the increase of the load on the top of pile and the height of the cave. 2）When unilateral overload is applied on the pile，all of the horizontal displacement of pile，earth pressure，elastic resistance and bending moment increases with the increase of overload and the height of cave. When the pressure at the top of the pile is zero，the lateral displacement of the pile decreases with the increasing depth，and it is maximal at the top of the pile. Both of the earth pressure and elastic re? sistance increase first and then decrease along the depth in the soil section. The bending moment of the embedded pile and pile impaling cave increase with depth，and it is maximal at the bottom of the soil layer. But it decreases af? ter entering the rock layer and cave. 3）Both of the vertical and horizontal bearing capacity of pile decreases with the increase of the height of the cave impaled by the pile. The pile section inside the cave formed by percussion drilling is not easily damaged by vertical compression and bend. Under the unilateral overload，the pile impaling cave is most likely to rotate around the soil-rock interface and bends at the bottom of the soil layer. In engineering，it is rec? ommended to increase the diameter and reinforcement rate of the upper pile in the soil layer and to embed the ex? panded section to an enough depth so as to improve the horizontal bearing capacity of the pile impaling cave.