In order to reduce accident risks caused by leakage during the refueling process, the hydrogen leakage and diffusion behavior of a 35 MPa hydrogen dispenser was numerically simulated using Ansys Fluent. The characteristics of hydrogen leakage and diffusion under the canopy structure in the refueling zone were investigated. The effects of leakage diameters, ambient wind velocity, and local ventilation on hydrogen concentration distribution and the evolution of flammable areas were analyzed. The results show that when the leakage diameter of filling hose is 2 mm, no flammable area is formed on the underside of canopy. However, when the leakage diameter increases to 5 mm and 10 mm, a flammable area can develop on canopy underside. The location of the highest hydrogen concentration on underside of canopy is concentrated near the axis parallel to the jet direction. Specifically, when leakage diameter is 10 mm, the hydrogen concentration on underside of canopy along vertical leakage direction exhibits a Gaussian distribution. When the ambient wind is perpendicular to leakage direction, wind velocities of 2 m/s and 8 m/s can effectively reduce hydrogen accumulation near the leakage hydrogen dispenser. In contrast, at the wind speed of 5 m/s, a vortex structure was formed near obstacles, leading to hydrogen accumulation and increasing the risk of fire and explosion. Under no ambient wind conditions, local ventilation is provided in the refueling zone. When the ventilation velocity reaches 5 m/s and 10 m/s, the hydrogen cloud concentration within the flow field can be successfully diluted to below the flammable limit within 2 s. Moreover, a ventilation velocity of 10 m/s shows a more pronounced effect in reducing the hydrogen concentrations in front of the leakage source.