In order to enhance the motion precision and reduce the initial error of the pitching mechanism which is used in the wind tunnel experiment, a novel error optimizing method was proposed. This new error optimizing approach is based on an improved ant colony algorithm. Firstly, three independent error sources which have influences on the motion precision of pitching mechanism were found and the mathematical models of three error sources including the radius of arc guide rail R, the length of connecting rod L and the installation position of linear guide rail yOa were established, respectively. The effect of each error source with the method of controlling variables was analyzed. Secondly, according to mathematical models of each error source, the mathematical model of three combined errors in the pitching mechanism was established. Based on the derived ant colony algorithm which is used in the error analyzing, the error optimizing problem could be converted to an optimizing problem of multiplied objectives. Finally, compared with results which utilize traditional Newton-Raphson iterative method, the motion accuracy of improved ant colony algorithm was higher, and the accuracy can reach a level of 10-5 mm. The compared results could also prove that the improved algorithm has a better global optimizing ability and it could avoid undesired effects of initial error in the structures when adopting the improved algorithm. The correctness and effectiveness of this method were confirmed by simulation with Matlab. In conclusion, the proposed approach was certificated to be effective and applicable in the engineering field.