Abstract: This paper presents a new type high-strength steel-concrete composite flat beam，its mechanical behavior is compared with the traditional composite flat beam，and the impact of steel strength on the new type composite flat beam is analyzed by using the large finite element software ABAQUS． The analysis shows that as compared with the traditional composite flat beams，the mechanical behavior of the new type composite flat beam is more superior． Under the same condition of sectional height and steel consumption，the load bearing capacity of new type composite flat beam is increased by 9. 7 percent，the stiffness increased by 0. 88 percent． The strength of steel has greater influence on the load bearing capacity than the stiffness of new type composite flat beam．