Abstract: In order to solve the problem about how to calculate the pressure loss through fire zone( PLTFZ) during fire case in longitudinal ventilation system design for underground road tunnels,a model for the PLTFZ was built based on thermodynamic balance,which yielded a semi-empirical formula.Model experiments and numerical simulations were used to validate the formula preliminarily,while a real project was adopted to illustrate the effect of PLTFZ on the pressure and air velocity distribution in the tunnel. The results show that given the critical air velocity,the PLTFZ is proportional to convective heat release rate and inversely proportional to the air velocity upstream and the tunnel cross-sectional area.And the formula is consistent with the correlation formula obtained from tunnel fire test and achieve close results,while it is better at clear theoretical foundation and air velocity values. It is necessary to consider the PLTFZ to make resistance calculation of ventilation system for underground road tunnels accurate and reliable,thus it develops an effective operation scheme for emergency ventilation,and after thorough verification the proposed PLTFZ formula can be used in the design calculations.