Abstract: cooling efficiency in the continuous casting. Usually it could be got from experiments or the experience,but it would take high cost,long period and hard difficulty. In this paper,the factors for controlling intensity were analyzed. The relevant equation between cooling intensity and water rate of flow,impacting velocity,droplet size was built. And the cooling intensity was calculated by the equation. The results show that there is a optimal air to water ratio,yet it is variable and decease with water pressure increase. It is very significant to reduce the energy consumption of second cooling in continuous casting.