By axial compression tests on 6 reinforced concrete slender columns wrapped with carbon fiber-reinforced plastic (CFRP) , with slenderness ratio ( SR) from 4.5 to 17.5, the results show that when SR increases the retrofitting effect declines. In the case of same SR, the stability coefficient ( SC) for the reinforced concrete (RC) columns with CFRP is much less than that without CFRP. There is 20% increase of stable bearing capacity to the former as compared with the latter when the SR in less than 17.5. The study summarized the simplified formula for SC, which provides a reference for engineering designers.