The invention relates to a motion arm forward kinetics positioning method based on an asymmetric variable structure. The method comprises steps that 1, parameter initialization is carried out in an operation space scope; 2, motion expansion of a motion arm composed of multiple asymmetric single modules connected in parallel is carried out to form translation rotation superposition operation of the multiple asymmetric single modules; 3, a relationship between parameters Li and thetai is designed; 4, according to a forward kinetics constraint equation, a transcendental equation is acquired through expansion, and a compact polynomial equation is acquired through utilizing angle parameter transformation; 5, according to an algebraic cancellation method, a final polynomial equation is solved through utilizing a parameter iteration mode; 6, key nodes of an angular expression are calculated; 7, according to a motion tail end pose vector expression of the variable geometric truss motion arm, and the desired position X and the direction n are calculated; and 8, primary positioning of a target pose is realized. Compared with the prior art, the method is advantaged in that measurement precision and empirical value stability of a system can be improved.