Abstract: The pile group is the main form of nuclear island structure in non-bedrock site. As the structure of the nuclear island has a large mass, large stiffness and concentrated mass distribution, the piles will have a high axial compression ratio. To study the seismic performance of the pile group with a high axial compression ratio, the cyclic lateral loading tests on the pile group in silty clay are carried out, and the failure mode and hysteretic characteristics as well as the variation law of pile deformation and internal force distribution are analyzed. The test results show that the compression-flexural failure mode occurs at the pile head, the connection between pile head and cap is the most serious, and the failure area extends to the depth of 5 times the pile diameter below the pile top. The relationship of plastic hinge length is as follows: front pile > back pile > side pile > middle pile. The inflection points of the front pile and the middle pile are between 1D and 3D below the pile top. The back pile has two inflection points, which are respectively between 3D~5D and 5d~7d below the pile top. The side pile has no inflection point. The deflection of the pile presents an inverted umbrella shape. At the elastic working stage, the load distribution proportion of the front pile and back pile is 24%, that of the side pile is 21%, and that of the middle pile is 10%.