In order to explore the influence of injection pressure on the deflagration characteristics of gasoline in the confined space, a 20 L spherical explosion test device was used to examine the changes of characteristic parameters, i.e., the transient flame propagation and temperature of gasoline mist deflagration under different injection pressures. The results showed that the optimum spraying time was 100 ms, and the maximum explosion pressure and maximum explosion pressure rise rate increased linearly with the increase of injection pressure, while explosion duration decreased linearly. The change of injection pressure had a more significant effect on explosion duration, and the combustion efficiency of gasoline increased significantly with the increase of injection pressure. Based on the colorimetric temperature measurement method, the flame temperature field was reconstructed. It was found that the maximum average temperature had a linear relationship with injection pressure, and the maximum average temperature increased with injection pressure. The influence of injection pressure on the deflagration characteristics of gasoline mist was analyzed through the changes of mist morphology and flame temperature during flame propagation. The outcome of this research can provide theoretical reference for the design of turbocharged direct injection internal combustion engine and the improvement of combustion efficiency and economy of gasoline internal combustion engine.