In order to improve the safety of vehicle-mounted liquid hydrogen storage and transportation, and reveal the leakage and diffusion characteristics of vehicle-mounted liquid hydrogen, a numerical simulation model was established to study the leakage and diffusion behavior of liquid hydrogen during transportation. The volume and distribution range of hydrogen clouds in different scene spaces were analyzed. The results show that the spatial structure of the liquid hydrogen leakage area has a significant effect on the diffusion trajectory of hydrogen gas. The airflow blocking effect in the building area causes hydrogen to closely adhere to the building walls and circulate upwards and on both sides. Although it changes the diffusion trajectory of hydrogen and inhibits its large-scale diffusion, the prolonged retention time of hydrogen around the building increases the level of danger. The hydrogen gas inside the semi enclosed tunnel is driven by buoyancy and collides with the top wall, accumulating in a "parachute" shape, forming a stable high concentration layer at the top and slowly diffusing in laminar flow along the longitudinal direction. The leaked hydrogen gas in the underground garage rises rapidly in a mushroom shape and fills the surroundings. Due to poor ventilation conditions, the volume of combustible gas clouds grows the fastest, and the potential risk of explosion significantly increases. Those results can provide theoretical basis for the safe transportation technology and intelligent control of liquid hydrogen in vehicles.