<p>In recent years, pile foundations have become the preferred choice for construction projects in the collapsible loess regions of northwest China. This is mainly because they can effectively mitigate the uneven settlement of building foundations, which is a common problem in these regions. However, the settlement mechanism of single piles in collapsible loess areas is complex, involving multiple factors that interact with each other. For the calculation of single pile settlement within collapsible loess areas, traditional methods primarily focus on the relative displacement at the pile—soil interface, while often neglecting the soil displacement outside this interface. This oversight can lead to inaccurate settlement predictions. Therefore, this paper presents a new single pile settlement calculation method. This method comprehensively incorporates the influence of negative frictional resistance and effective pile length. A three-line load transfer model is proposed to account for initial critical frictional resistance and lateral resistance softening. The relative displacement at the pile-soil interface is derived using the load transfer method, and the soil displacement outside the interface is calculated via the shear displacement method. A comprehensive settlement calculation framework applicable to collapsible loess areas is developed by superimposing these two components. Finally, field tests and numerical simulations were conducted to validate the method. The results show a strong alignment among theoretical predictions, measured settlement data, and finite element simulation results, confirming the reliability and practicality of the method.</p>