Aiming at the vibration evaluation of the support structure for a new reciprocating compressor installed on an offshore platform topside, the vibration evaluation criteria of the compressor support structure are proposed and the size of the model used in the analysis is discussed. The whole finite element model of the platform topside is established using ANSYS software and two partial models around the reciprocating compressor with different sizes are intercepted from the overall model, named PM1 and PM2. The evaluation of the frequency and vibration response of the compressor support structure is carried out to analyze the feasibility of the design scheme, and the calculation efficiency and accuracy of the two partial models are discussed. The results show that: the frequency and vibration levels of the supporting structure meet the evaluation criteria, that is, the design scheme is feasible; PM1 is of good accuracy and can greatly improve the calculation efficiency and can be used for vibration evaluation instead of the overall model during the structural foundation design; PM2 causes a larger calculation error, which is not recommended to use in the vibration evaluation of the offshore platform.