The discreteness is a common deficiency which impedes damage indices’ practical application. It is caused by the arbitrary linear combination and some missing necessary variables. In order to deal with this problem,the correction term was added to the widely cited Park-Ang damage index. The unknown parameters in the correction term were obtained by the maximum likelihood estimation of these parameters’ posterior distributions updated through Bayesian methodology. And the specimens for Bayesian updating were selected from PEER column database and Kawashima Earthquake Engineering Laboratory. Through model simplification process,a simplified modification was adopted,which has improved its goodness of fit to the experimental data. It has been found that the concrete core area and cross sectional area ratio,the longitudinal reinforcement ratio and the damage concentration factor are the critical variables affecting the error of the original damage index. It is caused by the arbitrary linear combination and some missing necessary variables. In order to deal with this problem, the correction term was added to the widely cited Park-Ang damage index . The unknown parameters in the correction term were obtained by the maximum likelihood estimation of these parameters’ posterior distributions updated through Bayesian methodology. And the specimens for Bayesian updating were selected from PEER column database and Kawashima Earthquake Engineering Laboratory. Through model simplification process, a simplified modification was adopted, which has improved its goodness of fit to the experimental data. It has been found that the concrete core area and cross sectional area ratio, the longitudinal reinforcement ratio and the damage concentration factor are the critical variables affecting the error of the original damage index.