Abstract: In order to study the characteristics of methane explosion pressure rise in confined space with weak con- straint and its propagation along the diffusion tube. A series of experiments were carried out on the characteristic pa- rameters of methane explosion at different volume fraction. The regularity of pressure increase in the confined space with weak constraint structure with different volume fraction of methane explosion was obtained. The research shows that the rise characteristic of methane explosion pressure in the space with the weak constraint is similar to the closed space,but the peak pressure is much smaller than the closed space. The maximum pressure of the fully enclosed space is 3. 2 times higher than the structure space with weak constraint. Due to the existence of constraint structure,when the volume fraction of methane is low,the blasting pressure is high,and the duration of high pressure in the cavity is short, while the duration of high pressure in the cavity increases when the concentration is close to the explosion equivalent. The propagation law of explosion pressure and flame in diffusion tube after film breaking was also obviously different as the change of methane volume fraction. Under the experimental conditions,when the methane concentration is low than 7. 0% ,the maximum time difference between the burst shock wave and the flame front is 5. 255 ms. The flame in the diffusion tube is mainly the expansive flame. Nevertheless when the methane concentration is high than 7. 4% ,the time difference is 28-40 ms. It suggests a second explosion of methane in the pipe,and the flame is mainly the turbulent flame. The propagation of explosion pressure can be divided into three situations. When the methane concentration is lower than 7. 0% ,the explosion pressure decreases with the increase of propagation distance. When the methane con- centration is 7. 4% and 11. 0% ,the explosion pressure increases linearly with the propagation distance. When the methane concentration is equivalent,its pressure propagation characteristics are identical to those of the gas explosion in the whole pipeline. The explosion pressure increases zigzag with propagation distance. The experimental results have reference significance for the prevention of explosion accidents and other gas burst with weak restrained structure dur- ing the overhaul of long gas pipeline,LNG and CNG storage tanks.