The invention provides an alternate iterative method and system for a hybrid multi-terminal direct current transmission system. The method comprises the steps of: obtaining AC system network parameters, node data, a converter control mode and a set value thereof, and according to a preset equation modification matrix, employing the alternate iteration method to calculate a hybrid multi-terminal direct current transmission system trend; and based on the trend calculation result, obtaining the active/reactive power of a multi-terminal direct current transmission system converter, wherein the converter comprises an LCC converter and a VSC converter, and the equation modification matrix is determined by Taylor series expansion based on a direct current system trend calculation model constructed by the LCC converter and the VSC converter.