Abstract: A gas explosion at 9. 5% concentration was performed in an experimental system and the images of propaga- ting flame were shot by a high-speed photography system in order to investigate the flame velocity of premixed gas / air mixture explosion. A new computational method of methane explosion flame propagation velocity was proposed based on the correlation coefficient between two adjacent flame images. Variation of gas explosion flame velocity of the whole process was obtained and the characteristics of dynamic changes were analyzed. The results indicate that the explosion flame undergoes a process of acceleration, deceleration, reverse acceleration, and reverse deceleration until it is quenched. Further research was performed by analyzing the details of explosion flame images and the flame propagation velocity of different regions in observation window. Comparison of two kinds of results proves that this method is accu- rate and reliable. The process of calculating the propagation velocity of gas explosion can be applied to the condition that flame is full of pipe.