CNG cylinder is a sort of used storage device in CNG filling stations. As a gas storage container with high-pressure, it will lead to harmful consequences if failure occurs. The explosion consequences after its leakage are analyzed in this article. The vapor cloud explosion (VCE) quantitative evaluation model is compared with API pub 581 consequences evaluation model. And the comparison of the consequences of the explosion bteween two evaluation models is also made based on an example with a set of CNG cylinders.