Abstract: Aiming at the quasi-static pressure characteristics of TNT explosion in closed tunnel under strong explosion, a quasi-static pressure calculation model based on energy conservation and ideal gas state equation is established in this paper, and a series of TNT internal explosion tests are carried out in the test tunnel. The results show that the quasi-static pressure of confined explosion is obviously affected by the chemical reaction of secondary combustion of explosive products. When Q/V is small, the theoretical calculation model could better estimate the quasi-static pressure after tunnel implosion. When Q/V is 0.234 k g·m^-3 and 0.463 k g·m^-3, the relative error between the theoretical calculated value and the measured value is only 4.6% and 1.4%. With the increase of Q/V, the proportion of explosive products participating in secondary combustion in the atmosphere of the tunnel decreases, and the proportion of quasi-static pressure increases decreases.