At present, the four-bar mechanism in the application of packaging thrust material, its motion trajectory and theoretical requirements are quite different, can not meet the needs of high precision packaging products. In this regard, the improved ant colony algorithm was used to optimize the geometric parameters of the four-bar linkage. Two dimensional coordinate systems were introduced to establish the geometric parameters of the four-bar mechanism. Coordinate equation of the trajectory points was derived through mathematical relations. The geometric parameter variables of the four-bar linkage were analyzed and the multi-objective optimization error function was constructed. At the same time, the motion constraint conditions of the four-bar mechanism were added. The improved ant colony algorithm was used have multi-objective optimization on the geometric parameters of the four-bar mechanism. The mathematical software Matlab was used to carry out the error simulation verification of the optimization results. The simulation results show that the average error and root mean square error of the four-bar linkage mechanism were reduced after optimization. The mean and root mean square errors of the crosswise were decreased by 55.9% and 59.1% respectively. The mean and root mean square errors of the longitudinal were decreased by 56.7% and 53.5% respectively. The improved ant colony algorithm could optimize the geometrical parameters of four-bar mechanism and improve the positioning accuracy of four-bar mechanism in packaging.