Experiments on gasoline-air mixture deflagration in the confined space with a local opening was carried out. Overpressure transients and flame behaviors under different concentration were acquired and the results showed that:there were two overpressure peaks inside the vessel but only one outside the vessel

and negative pressure zone was formed near the opening. The maximum value of internal and external overpressure were the same and both of them were caused by external deflagration. The value of overpressure peak showed the trend of first increasing and then decreasing with the increase of concentration

and the concentration corresponding to maximum overpressure peaks was 1.88%. The process of flame propagation could be divided into three stages

and the flame shape

color

duration of each stage

diameter of external fireball and average flame speed were dominated by initial concentration. With the increase of the concentration

the blue laminar flame with smooth front was changed into bright yellow flame with wrinkled front

and the duration of laminar propagating stage as well as accelerating and distorting stage showed the same trend of first increasing and then decreasing

but the duration of extinguishing stage showed a decreasing trend. The relationship between the diameter of fireball and concentration could be fitted by cubic polynomial

and the flame speed of 1st and 2nd stage could be fitted by quadratic polynomial. With the increase of opening ratio

the pressure peaks and flame speed of 2nd stage showed a decreasing trend

and the diameter of fireball showed a first increasing and then decreasing trend.