Abstract: A loading system of hybrid testing based on OpenFresco was established to study the effectiveness of the system. A hybrid test of a 1/2 scaled three-story high strength steel composite K-eccentrically braced steel frame (K-HSS-EBF) was conducted to investigate the seismic performance of the structure model. The effectiveness of the test system is studied by preloading the specimen under small load conditions. The displacement loading precision of the experimental substructure and the loading time difference of the actuators are analyzed. The natural frequency, displacement response, horizontal seismic force, hysteretic behavior and the strain of key parts were obtained from the hybrid test. The results show that the peak displacement of the actuator is close to the calculated peak displacement. The maximum relative error is 13.60% and the average loading time difference of the actuator was kept at approximately 20 ms under different conditions. With the increase of the seismic peak acceleration, the natural frequency decreases and the stiffness of the structure degrades slightly. The deformation of each story is mainly in the web of the energy dissipation beam, which is mainly shear deformation. The maximum inter-story drift of the model structure under the frequent and rare earthquakes are 1/1068 and 1/197, respectively, which meet the inter-story drift limit in the seismic design code for buildings. In conclusion, the hybrid test system based on OpenFresco can better respond to the seismic response of the structure and the K-HSS-EBFs have good seismic performance.