Abstract: Taking the negative pressure deformation of coke tower's overflow water tank of some refinery as an example, the accident cause and problems existed in equipment are analyzed.In the first, overflowing operating initiats when water is not yet fulfilled the coke tower, vast vapour enters into storage tank, which results in the tank's pressure going up, secondly, high-temperature overflow water with vapour and oil vapor simultaneously enter into the tank, and tank level rise, which further lead the inner pressure of tank to rise; and afterwards, low-temperature water drained off from coke water soaking process enters into the tank, condensation volume of vapour and oil vapour in it rapid contract, which result in negative pressure deformation of the tank.Based on above analysis results, rectification method and precaution measures are put forward from technical improvement, process design and selection of breather valve.