As an important energy resource, acetylene (C2H2)has a huge explosion risk during its production, storage and utilization processes, for the leaked C2H2would easily blend with ambient air to form explosive mixtures, causing serious explosion accidents in the presence of ignition sources. A self-designed gas explosion facility were used to investigate the flame propagation behaviors and explosion characteristics of C2H2/air with different equivalence ratios (φ) under a weak constraint. Experimental results showed that with the increasing equivalence ratio, the amount of carbon black increased, resulting in the flame colors changed from light blue to khaki, and the decay rate of the maximum explosion pressure decreased gradually. The average flame propagation velocity and flame temperature reached the maximum value of 14.16m/s at φ=1.32and 3617 K at φ=1.96, respectively. With the static placing time enlarged, the explosion pressure change trend could be divided into three stages of "falling-standing-rising". The results would help to provide the damage data of thermal and shock wave for acetylene explosion prevention, and develop preventive measures to improve the safety of acetylene application process industry.