The aim of this paper is to investigate the water pressure effects on hydraulic fracture behavior of concrete with wedge-splitting testing under dynamic loading. Five waterproof strain gauges are stuck along the crack path to observe the fracture process during the experiments. Four silicon water pressure sensors successfully measured the water pressure value on concrete face. The results show that the water pressure on crack faces accelerates the crack propagation of the concrete. The critical values of the splitting force decrease 26.7 and 25.6%, respectively, with the external applied water pressure of 0.2 and 0.4 MPa. Moreover, the hydraulic crack propagation speed increases at the beginning and tends to reach a peak value finally. The peak value of cracking speed is 11.08 m/s, which is high. Under dynamic loading, the water fails to fill the crack and only the trapped water interacts with the crack face. The water pressure is mainly a parabolic curve distribution along the crack path and the peak value decreases with the increase in the crack length.