A tank container employed for the transportation of dangerous chemicals was discovered to have leakage at the bottom during road transport. Upon inspection, it was determined that the leakage point was the area on both sides of the loading and unloading valve at the rear of the tank. The causes of the cracks in the tank container were analysed through chemical analysis, metallographic inspection, and scanning electron microscopy. It was identified that the bottom support plate near the unloading port of the tank container endured dynamic loading for an extended period during transportation, generating fatigue cracks in the stress concentration area of the support plate. Under the continuous influence of the loading, the crack gradually extended along the weld joint area to the tank body, eventually leading to penetrating cracking of the tank body.