The shear-plane ejection mechanism plane linkage is propelled by horizontal movement of the cylinder-piston which uses high pressure air as the power source to promote the missile to move vertically downwards, completing mandatory separation of missile and launcher. The processing and installation error of the ejection mechanism will affect the separating attitude of the missile directly. Based on modeling the ejection mechanism, the matrix was used to analyze the position error of the ejection mechanism. After analysis of different parameter of the mechanism, a greater impact on the position error of the mechanism was found out; this provided a theoretical basis for designing and controlling the precision of the ejection mechanism.