For the purpose of making a more accurate study on the interface mechanical properties of the frozen soil from more perspectives, improvements on the original multi-function direct shear apparatus for frozen soil are conducted, which involve improvements on temperature collecting and recording device, displacement measuring device, and loading and unloading device for frozen soil box. These improvements will allow the direct shear apparatus to better meet testing requirements on the interface mechanical properties of frozen soil. Based on the original direct shear apparatus, modules related to the adfreezing strength test on the interface of frozen soil and the mechanical property test on the interface layer of frozen soil are integrated, meeting the multi-function testing requirements. The new functions are developed by means of modular design, in which the compatibility and convenience of switching between different functional modules are emphasized. The experimental results have shown that the improved direct shear apparatus is able to meet the multi-function experiment requirements for the frozen soil, such as the research on the adfreezing strength and mechanical properties of interface layer, and the testing data is demonstrated to be stable and reliable.