Abstract: In order to investigate the seismic performance of circular timber columns strengthened with near surface mounted steel bars and wrapped CFRP (carbon fiber reinforced polymer) strips, and to propose the calculation method for the lateral performance of strengthened timber columns, 5 timber columns with composite reinforcement were tested under lateral cyclic loading, with the number of mounted steel bars and wrapped CFRP strips as variables. The test results indicated that the composite reinforcement method could delay the damage process of timber columns, and the specimens showed tensile rupture of timber grain near the bottom section, indicating significant brittle failure. The bearing capacity and deformation performance of strengthened timber columns were improved obviously. Furthermore, with the increase of wrapped CFRP strips, the peak load and ductility of specimens showed trend of improvement, and the position of the mounted steel bars could influence the bearing capacity of timber columns. The distributions of strain-displacement hysteretic curves of steel bars and CFRP strips were almost consistent with the corresponding curves of timber, which denoted that the strengthening materials could deform and work together with timber, and improve the hysteretic performance of timber columns. The strip method was adopted for the force analysis of the specimen’s cross section, and the reliability of the internal force analysis was verified through the comparison between theoretical calculation and test results. Based on the materials mechanics, the calculation method for the lateral performance of composite strengthened timber column was proposed, and the theoretical results were in good agreement with the experimental data.