Abstract: In order to study the failure mechanism of RC columns strengthened by CFRP subjected to axial and cyclic lateral loads, a three-dimensional meso numerical model of reinforced concrete square columns strengthened with CFRP is established, considering the heterogeneity of concrete materials and the bond slip between reinforcement and concrete. On the grounds of the good agreement between the meso-scale simulation results with the available experimental results, the section size of the specimens is enlarged. Furthermore, the effects of axial compression ratio, volume allocation rate of CFRP on the aseismic performance and size effect on shear strength of reinforced concrete short columns strengthened with CFRP are explored. The results show that: the bearing capacity of specimens increases as the increase of axial compression ratio, but the ductility decreases; increasing the volume allocation ratio of CFRP has a limited effect on the increase of bearing capacity, which will enhance the ductility of columns; with the increase of specimen size, the nominal shear strength of columns tends to decrease, and there exists size effect behavior.