In this paper, the deflagration region and characteristics of the hydrogen flow which was generated by high-pressure hydrogen discharge from storage vessels were studied. A 3-D analytic model is established based on the species transfer model and the SST k ? turbulence model. The established model is applied to the research of the flow characteristics of the hydrogen under-expanded jet under different filling pressures of 30 MPa, 35 MPa and 40 MPa, respectively. The evolution process of hydrogen combustible cloud is analyzed under the filling pressure of 30 MPa. It is revealed that a supersonic jet is formed after the high-pressure hydrogen discharge outlet. In the vicinity of the Mach disk, the hydrogen jet velocity and temperature reach the maximum values, and the variation of filling pressure has little effect on the peak values of the hydrogen jet flow velocity and temperature during the considered pressure range. In the rear of the Mach disk, the variation rates of the hydrogen flow velocity and temperature are in inversely proportional to the hydrogen filling pressure. At the preliminary stage, the discharged hydrogen is apple-shaped, which expands along the radial, and then the axial growth rate of the hydrogen cloud increases with the passage of time.