Experiments were performed to examine the overpressure change laws and flame speed change laws both in a closed straight pipe and a closed pipe with a T-shaped branch structure. The effects of T-shaped branch structure on the maximum overpressures, overpressure rise rates and flame speeds of gasoline air mixture explosions were deeply investigated. It was found that the maximum overpressures increased with the growth of distance from the ignition point both in the two kinds of pipes. Oscillations of the flame front were observed during the flame development. The maximum flame speeds were found in the range of 52%-63% of the pipe length for the straight pipe, and 59%-64% of the pipe length for the pipe containing a T-shaped branch structure. Experiments also showed that the T-shaped branch structure had the ability to enhance overpressures, average overpressure rise rates and flame speeds, and it had little effect on the upstream flow of T-shaped junction, but much on the downstream flow, and when initial concentration was at 1.7% (close to the stoichiometric concentration), the degree of enhancement was more significant than 13% (lean concentration) and 2.3% (rich concentration). In addition, the images by a high-speed camera showed that when the flame propagated through the section of T-shaped branch structure, distortions and winkles of the flame front could be observed, which increased the flame surface area, thereby increasing the burning rate, heat release and flame speed. (C) 2016 Elsevier Ltd. All rights reserved.