The invention relates to the technical field of cooling towers and discloses a design method of a natural draft cooling tower water distribution system. The design method includes the following steps that S101, basic parameters are input and saved in a database; S102, the inner and outer partition boundary, the sprayer position and the water distribution pipe water distribution route are determined, and a calculation model is built; S103, the water distribution pipe diameter and the sprayer type are preliminarily calculated; S104, data needed by water distribution calculation is read from the database; S105, water distribution calculation is carried out, and calculated result data is loaded in the calculation module; S106, the calculation result is analyzed, the water distribution uniformity is checked, if the condition is met, S107 is executed, or else, a corresponding model is corrected, and then S104 is executed again; S107, a three-dimensional real model is generated according to the calculation model; S108, a material report is automatically generated; S109, a construction drawing is automatically generated. The design scheme of the water distribution system is visual, efficient and accurate.