Abstract: lt is related here what should be done before welding the leaked location at the bottom of metal storage tanks in caves. Six steps are suggested. They are: make the tanks concerned thoroughly empty, separate from the others with a wall, discharge the oil gas, flush oil dirties, and find out the leaked part and points to be welded. Specific methods, requirement and notises each are dealt with, toge-ther with some personal expriences and lessons.