Numerical simulation of TNT explosion in air was performed by AUTODYN software. Post-detonation burning effect in negative oxygen balance explosive was considered in the numerical calculation model. Calculated results including peak overpressure,specific impulse and positive time were compared with that calculated by similitude equations and experimental data from Baker. Results show that airblast peak overpressure near explosive calculated by Brode equation is much larger than that AUTODTN software and Henrych equation, because the peak pressure of airblast can not be distinguished from that of detonation products.