To improve the seismic performance of new structure with assembly-situ walls, experiment and finite element analysis were applied to 2 models under vertical loads, the stress, cracks, deflection, failure patterns and out-of-plane displacement were studied. Results indicate that the structure shows superior strength and rigidity under normal loads, the out-of-plane instability does not happen but a lag appears as destruction. In addition, the composition between precast shell and cast-in-situ columns shows excellent connection performance and does not slip. The precast shell can significantly improve bearing properties. Meanwhile the “optimal size” section has capability to promote compressive behavior. In conclusion, the new structure is testified to meet reliability requirements; the out-of-plane instability does not appear in normal storey height structures under gravity loads.