To study the collapsible deformation development of the compacted loess foundation and the reliability of existing calculation methods for collapsible deformation, the indoor loading- wetting model test was carried out on the compacted loess foundation in Yangling. The collapsible deformation was calculated using the one- dimensional collapsibility coefficient method, chord modulus method, and tangent modulus method. The calculated results were then compared with the measured results. The experimental results show that collapse deformation occurs quickly after the foundation is wetted and then reaches stability. Due to non- self- weight collapse, collapse deformation occurs mainly in the top layer of the loess foundation. Calculated results of the three methods show that under a small load, the collapse deformations calculated by the one- dimensional collapsibility coefficient method without considering lateral extrusion are close to the measured values, while the deformations calculated while considering the modification factor of lateral extrusion are greater than the measured values. Under a large load, the collapse deformations calculated by the one- dimensional collapsibility coefficient method with and without considering the lateral extrusion are far less than the measured values. The chord modulus obtained from the in- situ loading test is unsuitable for calculating the collapse deformation of the compacted loess foundation. Since the elastic deformation of the initial yield surface is not well considered, the collapse deformation calculated by the tangent modulus method is greater than the measured value.