Abstract: Studies the main manufacturing characteristics(site error and longitudinal form error of the gear) and their influence on the whole mechanism.The coupling impact of the two errors to the whole mechanism is studied with the method of orthogonal test and FEM.The extrema of the two errors are obtained.Finite element model of the microminiature clock mechanism is established.The model with the combination of the site error and longitudinal form error which impact the mechanism seriously is analyzed with FEM, so as to verify the rationality of extremum and supply reliable basis for the designing, machining, detection and assembly of parts.