The　seismic　failure　mechanism　of　underground　structures　presents　that　the　insufficient　lateral　deformation　capacity　of　central　columns　will　result　in　the　collapse　of　the　overall　structure.　Therefore,　this　study　proposed　applying　Polyethylene　Terephthalate　Fiber-reinforced　Polymer　(PET　FRP)　to　enhance　the　lateral　deformation　capacity　of　the　central　columns　of　underground　structures　and　then　improve　the　seismic　capacity　of　the　overall　structures.　The　numerical　models　of　PET　FRP　retrofitting　reinforced　concrete　(RC)　columns　subjected　to　high　axial　loads　and　increasing　cyclic　deformations　were　verified　by　experimental　results.　With　the　calibrated　models,　the　inter-story　deformation　capacity　of　the　underground　structures　with　and　without　PET　FRP　retrofitting　was　contrastively　analyzed,　and　the　seismic　response　of　the　two　underground　structures　subjected　to　both　horizontal　and　vertical　ground　motions　was　simulated　and　discussed.　It　was　found　that　the　PET　FRP　retrofitting　structure　experienced　smaller　earthquake　threats　due　to　the　larger　lateral　deformation　capacity.　Furthermore,　the　repairability　of　the　PET　FRP　retrofitting　underground　structures　after　earthquakes　was　also　investigated.　Numerical　results　presented　that　applying　PET　FRP　retrofitting　central　columns　of　underground　structures　could　improve　the　seismic　performance　of　overall　underground　structures.