With the increase in the number of transformers., the internal transformer oil fire protection is severe. Under various situations., the effectiveness of foam extinguishing agent in suppressing fires varies substantially. This research establishes a targeted evaluation index system appropriate for transformer oil fire based on the relevant national standards and researches., and then formulates the value standard of each index based on the relevant national standards and experimental data in order to choose the most suitable foam fire extinguishing agent for transformer oil fire. The research then uses the entropy weight TOPSIS approach to evaluate the applicability of three different types of foam extinguishing agents based on the index system. The results demonstrated that fluoroprotein foam performs most effectively overall. As a result., choosing fluoroprotein foam as the substation foam extinguishing agent is advised.