Abstract: The basic theory and engineering application of the undergraduate textbook of Engineering Fluid Mechanics are applicable to circular pipelines, while for the calculation of non-circular pipelines, the equivalent diameter method is mentioned in the textbook, which considers that the resistance of non-circular pipelines is similar to that of circular pipelines with the same equivalent diameter, so that non-circular pipelines are calculated according to circular pipelines. But the resistances of circular pipelines with the same equivalent diameter and non-circular pipelines behave very differently under different conditions. Therefore, this paper uses numerical calculation method to analyze the factors affecting the specific friction of rectangular section pipelines, and provides a basis for the resistance calculation of special-shaped pipelines.