The invention belongs to the technical field of microwave passive device CAD, and in particular relates to a computing method of multi-catastrophe structure arbitrary section complex power, and is based on a mode matching method. By use of the method disclosed by the invention, the tedious solution of an electric field and a magnetic field is avoided, and the computer resource consumption and computing time are reduced; the complex power of an arbitrary section can be obtained by direct use of scattering matrixes of catastrophes at all levels, and a simple and effective verification mode is provided for the accuracy of a mode matching method application. The complex power value of the arbitrary section in the multi-catastrophe structure can be rapidly and accurately obtained, and the method is a fast and effective computing method which is convenient for operation.