In order to investigate the relationship between active earth pressure and displacement of PC piles, and subsequently predict and evaluate the safety of PC piles during foundation pit excavation, a sectional fitting function was employed to establish a calculation formula for active earth pressure in retaining structures considering displacement. The effectiveness of this formula was verified by comparing it with experimental data. The ratio of steel pipe pile diameter (D) to steel sheet pile width (W) was defined as the shape coefficient of PC piles. A finite element model using Flac3d finite difference software was developed to analyze the influence of PC pile section shape on lateral soil pressure distribution under excavation conditions. The results indicate that the proposed calculation formula for non-limiting active earth pressure considering displacement accurately reflects the relationship between non-limiting active earth pressure and displacement in retaining structures with flat surfaces. As displacement increases, there are differences in lateral earth pressures between the steel plate part and steel pipe part of PC piles. When the shape coefficient is 1, the earth pressure on the steel plate side exceeds that on the steel pipe side; however, when it is 2 or 3, the opposite occurs. The active state earth pressure on the steel pipe side decreases with increasing shape coefficient, while that on the steel plate side increases accordingly. Additionally, both depth and ratios between diameters of steel pipe piles and widths of steel sheet piles affect shape coefficients for PC piles; specifically, when these ratios are equal, higher depths result in lower shape coefficients. Introducing a shape correction coefficient allows for differentiation in lateral earth pressures among different parts of PC piles. In practical engineering, the horizontal displacement of PC piles at different depths can be measured using a deep horizontal displacement tester. The soil pressure can then be calculated using a formula to obtain the distribution of bending moment in the pile, which enables evaluation of the safety of PC piles during excavation.