<p>Collapsible loess is prone to significant deformation under the influence of water and load, leading to severe engineering problems and disasters. Compaction pile, a common method to address loess collapsibility, often suffers from design inefficiencies. In order to address this issue, it is necessary to quantitatively evaluate the collapsible deformation after compaction treatment. This paper introduces the concept of the compaction coefficient, derived through theoretical analysis based on the SMP strength criterion and the associated flow rule. The impact of soil parameters on the compaction coefficient is examined. Using indoor model tests of pile sinking and compaction combined with electron microscope scanning, the compaction coefficient at various positions between piles is determined. The numerical calculation results from subroutine development are compared with theoretical and experimental findings, verifying the accuracy of the proposed compaction coefficient. Additionally, indoor collapsibility experiments establish the relationship between the collapsibility coefficient and the compaction coefficient, as well as the variation of the collapsibility coefficient with pressure, which is then incorporated into a programming language. Finally, a numerical calculation method for collapsible deformation based on the Abaqus subroutine is proposed and validated through indoor model collapsibility experiments.</p>