Abstract: To study the structural behavior of precast ultra-high performance concrete (UHPC) and post-cast normal strength concrete (NSC) composite beam,9 groups of UHPC-NSC composite specimens and 9 groups of C40-NSC composite specimens were designed for four-point bending tests.The test variables included UHPC/NSC thickness ratio,precast UHPC slotting density and compressive strength of post-cast NSC.The results show that the precast UHPC with grooves has a good bond to the post-cast NSC to ensure that the two work together.Section of composite specimen approximately conforms to plane section assumption in bending deformation process.Precast UHPC has better crack control ability than C40 concrete,the mid-span deflection of the UHPC-NSC composite specimens is smaller than that of C40-NSC specimens under the same load.Compared with the C40-NSC composite specimens,the flexural strength of UHPC-NSC composite specimens is improved by 9.10%~78.78%.Within the range of slotting density of this test (2.5~4.5),the failure modes of UHPC-NSC composite specimens is divided into flexural and shear failure modes.The formulas for predicting the ultimate shear strength and flexural strength of UHPC-NSC composite beams was proposed.