Abstract: Recently, earthquake-affected areas are increasing worldwide. Especially, buildings that are not designed to be earthquake resistant may be vulnerable to earthquakes and various reinforcement methods are being applied to improve seismic performance. In addition, structures that penetrate buildings such as roads and subways also need to be reinforced by vibrations such as earthquakes. This this research, therefore, aims to develop CFT column strengthening method with excellent seismic performance, so that, there is no damage caused by collapse in buildings where periodic vibration and earthquake occur. The seismic retrofit method of the CFT (Concrete Filled Tube) columns is a method in which CFT connectors are installed on the surface of a conventional reinforced concrete member first then the CFT columns are welded and integrated into the joint device, finally, high-performance mortar is injected to improve the seismic performance of existing reinforced concrete. For the performance test, we propose structural simulation and excess water removal method to improve the concrete performance inside the CFT column.