The cracking problem of concrete in the negative moment zone of steel box concrete composite continuous beams has affected the development of such composite structures towards larger spans. In response to this issue, a new technology of applying external cables in steel box concrete composite continuous beams is proposed, and the beneficial effect of applying external cables on enhancing the crack resistance of concrete in the negative bending moment zone of steel box concrete composite continuous beams is studied, improving the elastic-plastic structural performance of steel box concrete composite continuous beams. Through comparative experiments, it has been shown that after the application of external cables, the cracking load of concrete in the negative bending moment zone of the steel box concrete composite continuous beam increases by 2.8 times, the elastic-plastic bending stiffness of the composite continuous beam increases by 29.35%, the bearing capacity increases by 34.67%, and the structural performance is significantly improved. On the basis of experimental research, the relationship between the local mechanical properties in the negative moment zone of the steel box concrete composite continuous beam and the overall nonlinear structural performance is analyzed, revealing the mechanical essence of external cables improving the elastic-plastic structural performance of the steel box concrete composite continuous beam, and providing suggestions for bearing capacity calculation. The research results can serve as a reference for the engineering application and theoretical analysis of external cable steel box concrete composite continuous beams