This paper deals with the mechanical properties of C40 concrete with a steel fiber dosage of 0～2.0%,and discusses the mechanical properties and economical efficiency of size-variable composite concrete with optimal volume ratio.The results show that the compressive strength of the steel fiber-reinforced concrete increases with the dosage of steel fibers,that the compressive strength increases by 27% and the flexural-tensile strength increases by 50% at the dosage of 1.5%,that the addition of steel fibers makes the load-displacement curve of the concrete change from elastic mode to elastic-plastic mode and improves the brittle fracture of the pavement,and that the two-layer composite concrete composed of steel fiber-reinforced concrete（with a steel fiber dosage of 1.5%） and common concrete in a thickness ratio of 1∶ 3 is of high strength,good anti-deformation ability and high economic benefit.