Abstract: The emergency situation of hydrogen long-tube trailer occurs in a urban road tunnel is prone to cause hydrogen leakage and explosion accidents. In this study, a numerical model of hydrogen long-tube trailer accident in tunnel is developed based on the real scenario, and the mechanisms of accident evolution and damage effect are then elucidated through the collection and analysis of characteristic parameters (such as dispersion concentration, overpressure and temperature, etc.). The results show that the leaked hydrogen disperses in a vertical plume at the tunnel entrance and accumulates in a certain area when it disperses inside the tunnel, while its dispersion velocity is related to ventilation condition of tunnel. A coupling effect is generated between shock wave and flame induced by such hydrogen long-tube trailer explosion in tunnel, resulting in even larger damage to the tunnel.