In engineering construction, it is an economical and efficient design scheme to combine the tower crane foundation with the basement raft and use the existing structure piles as the foundation piles of the tower crane. In order to accurately analyze the force on pile top of the pile foundation with the tower crane eccentrically set on the rectangular cap, new calculation formulas are derived theoretically, and the change law of the force on pile top when the tower crane rotates is analyzed. The results of the simplified solid finite element model in ABAQUS and the theoretical formulas are compared to verify the accuracy of the theoretical formulas. The formula in the current Technical Standard for Tower Crane Concrete Foundation Engineering (JGJT 187—2019) is only applicable when the pile foundation cap is close to square. For rectangular pile caps with a relatively large aspect ratio, it is more accurate and safer to calculate the force on pile top using the theoretical formulas proposed in this paper.