In　this　paper,　a　method　is　proposed　for　using　accumulated　ductility　coefficient　to　evaluate　the　required　deformation　capacity　of　reinforced　concrete　piloti　buildings.　Based　on　the　relationship　of　energy　conservation　during　a　major　earthquake,　a　formula　is　deduced　for　calculating　the　required　deformation　capacity　of　the　soft-first　story.　In　order　to　affirm　the　calculation　results,　an　elasto-plastic　analysis　was　carried　out　for　a　multi-degree　of　freedom　system　subjected　to　some　actual　earthquake　ground　motions.　The　calculation　results　from　the　formula　were　compared　with　the　analysis　results.　The　conclusions　show　that　the　proposed　formula　can　well　and　safely　predict　the　required　deformation　capacity　of　the　piloti　buildings.