The calculation of water distribution in the cooling tower is an indispensable procedure for its design. However, the current one-dimensional hydraulic calculation method based on the Bernoulli equation and the continuity equation needs to solve large-scale set of equations,which consumes a large quantity of work. In view of this,a new method simplifying a water distribution pipe as a water resistance unit was proposed,and the mathematic model for the calculation of the equivalent resistance coefficient of the water resistance unit was built. By applying the model,the water distribution system could be simplified as a simple hydraulic system which consists of a main pipe and several water resistance units. This turned the optimal calculation of the pipe into the optimal calculation of the water resistance unit so as to successfully decouple the global system optimization with the pipe local optimization. The validation of the proposed method in an engineering example showed that the calculation result of the proposed method was consistent to that of the current method,which could satisfy the design requirement. In addition,as the model is simple and convenient to program, which can significantly reduce workload, it is worth being applied in the future projects.