Abstract: The sealability of a canister cover was failed in turnover period. The causes of sealability failure of the canister cover were analyzed by means of physical and chenical examination, failure simulation experiment and so on. The results show that the cracks on the outer surface of canister cover caused by the mechanical force in turnover period extended and led to leakage failure. Increasing the thickness of the buffer material in the packing box and making the gap between the canister and the buffer material within 1 mm could effectively avoid this kind of failure.