Abstract: The safety of tank farm shall be guaranteed, but safety means cost. Therefore cost and benefit analysis shall be made to prevent unlimited investment on safety. Through analyzing the relationship between cost and benefit for the tank farm as well as tank farm safety, it is pointed out that tank farm shall be appropriately safety guarded to achieve maximum overal benefits and minimum safety costs and failure damages, and that safety measure shall be taken on the basis of optimal subject to be achieved. While unsafe status of matters is a critical factor for tank farm failure, unsafe human activity is another factor giving rise to tank farm failures.