By testing the properties of 47 LYP100 low yield steel specimens under both monotonic and repeated tensile loading, the stress strain curve, load displacement curve, skeleton curve, failure mechanism and ductility characteristics of each specimen were studied. The results show that the cross sectional thickness of specimens is the main factor affecting the energy consumption of steel, and the energy dissipation capacity of 12mm thick specimens is much better than that of 6mm specimens. The welded joint has an adverse effect on the damage of the specimen. The fatigue damage accumulation effect of specimens with welded joint under cyclic tensile loading is significant, and brittle fracture is prone to cause the ductility of the test piece to deteriorate. After the low yield point steel LYP100 is welded with Q345 steel or Q460 steel, the strength of specimen is improved, and the strength hardening phenomenon under the cyclic tensile load is obvious, but the ductility is deteriorated.