To explore the explosion characteristics of propylene oxide mist， a 20 L spherical liquid fuel explosion test system was used to study the effects of ignition delay time and mass concentration on the explosion characteristics of propylene oxide/air mixture. At the same time， high-speed cameras were used to photograph the flame propagation process， the dynamic distribution images of flame temperature field was reconstructed by colorimetric pyrometer technology and the effect of mass concentration of propylene oxide on the flame temperature was discussed. The experimental results showed that with the increase of ignition delay time， the maximum explosion overpressure and the rise rate of maximum overpressure increased first and then decreased， while the combustion duration was on the contrary. The optimal ignition delay time was 100 ms with the maximum explosion overpressure reached 0.89 MPa. With the increase of the mass concentration of propylene oxide，the maximum explosion overpressure， maximum overpressure rise rate and maximum average flame temperature were all initially increased and then decreased. When the mass concentration was 498 g·m^-3， the maximum explosion overpressure and maximum overpressure rise rate were both the highest， which were 1.02 MPa and 60.91 MPa·s^-1， respectively. But the mass concentration corresponding to maximum average flame temperature was significantly lower than that of maximum explosion overpressure. When the mass concentration was 415 g·m^-3， the flame average temperature reached the maximum value of 1937 K. The research results can provide reference for optimization of detonation performance and evaluation of damage efficiency of the fuel air explosive.