To investigate the relationship of strain between the high strain-hardening UHPC and the reinforcement when the flexural failure of beams occurred, one-third loading experiments were carried out on five girder specimens. During the tests, the change parameters of the specimens are the reinforcement percentage and the type of reinforcement. Firstly, the load-deflection curves of reinforcement and high strain strengthening UHPC indicate that T-beam failure process could be divided into three stages: the elastic stage, the fracture development stage and the load-to-failure stage. Secondly, the cooperation between reinforcement and UHPC was discussed based on the load-strain curves of reinforcement and high strain-strengthening UHPC. Finally, the loading process was divided into four stages according to the stress-strain curves of reinforcement and high strain-strengthening UHPC. The results show that the reinforcement rebar and the UHPC present reliable cohesiveness and could keep the strain consistent before the reinforcement reaches the yield strain. The resistance of high strain-hardening UHPC tensile strength plays more important proportion than reinforcement rebar during the flexural process, and it could be bigger at a low percentage of reinforcement. It is suggested that the tensile strength of UHPC should be taken into account when calculating the bearing capacity of high strain-hardening UHPC, and ensure the accuracy of the calculation method of bearing capacity.