Abstract: During the construction of offshore platforms, many equipment needs to be installed by side loading because of the delay of arrival time. In this paper, taking the low temperature separator of a large gas mining center platform in the South China Sea as an example, a kind of equipment side loading auxiliary platform is designed, and the mechanics analysis of the structure in different working conditions is carried out by SACS software. The results show that the strength of the auxiliary platform is satisfied with the construction requirements, the strengthening connection should be adopted between the deck and the platform. The influence law of the structural form of the supporting structure on the force is analyzed. It is found that the frame structure can effectively improve the overall strength and the anti deformation ability of the supporting structure, and can directly reduce the deformation by nearly 44%, and it has a definite reference value for the design of the auxiliary platform for equipment side loading.