Abstract: A company's gas storage tank experienced a cracking and leakage accident after less than 1 year of use. The causes of cracking in gas storage tanks were analyzed using macroscopic observation, chemical composition analysis, scanning electron microscopy and energy spectrum analysis, metallographic examination. The results show that the leakage point was located at the fillet weld between the inlet pipe of the gas storage tank and the cylinder. Due to excessive welding heat input, the base material on the pipe side was severely overheated, and the microstructure transformed into a Widmannstatten structure, resulted in insufficient toughness of the corner weld joint. Under the joint action of welding residual stress and working stress, microcracks were initiated near the fusion line of the weld, and the cracks preferentially extended in the heat affected zone, ultimately led to brittle cracking of the gas storage tank weld.