Taking a fiveaxis vertical grinder as an example, the method for analyzing the sensitivity of geometric error is proposed. Based on the theory of multibody system and the principle of homogeneous coordinate transformation, 33 geometric errors model of fiveaxis vertical grinder was established, and the mathematical model of error sensitivity analysis was given by using the derivative method. And the key geometric errors were identified according to this model, the variation law of the key geometric errors sensitivity coefficient with the motion of translation axis was studied. The research results provide a theoretical basis for improved design and realtime error compensation of precision machine tool.