Abstract: In wet sulfureted hydrogen environment, hydrogen corrosion of 4-kind of cracking types, that is, HB, HIC, SSCC and SOHIC will probably produce in LPG tanks, however, grade estimation method of cracking type is only mentioned partially in TSG R7001-2004《Regulation on Pressure Vessel Regular Inspection》. Origins for different hydrogen corrosions in wet sulfureted hydrogen environment are analyzed. It is pointed out that after inspection of LPG tank, grade estimation of safe condition on HB, SSCC and SOHIC should be carried out individually. As for HIC, the estimation should be made based on its developing condition in wall thickness direction of pressure vessel by referring to that of HB or SOHIC.