In order to rapidly and accurately design the rudder gear and determine the sizes of its main components at the beginning of project design, the relevant calculation requirements for rudder system in the rules of several major classification societies are researched and contrasted, their general requirements are summarized, and the conclusion is drawn that it is necessary to design the rudder gear by the direct calculation plan. According to the methods, such as structural mechanics model decomposition, rules check, etc., it is verified that the direct calculation method can be directly used in the design of rudder gear and size determination of its main components.