The invention belongs to the technical field of manufacturing of aeroengines and relates to a part sectioning position selection method, in particular to a method for selecting a longitudinal mounting position of a split casing. The method includes the steps: step one, determining stress measurement points of an annular workblank; step two; subjecting the stress measurement points determined at the step one to stress measurement; step three, selecting the point highest in stress value as the longitudinal mounting position of the split casing. By adoption of the method for selecting the longitudinal mounting position of the split casing, scraps of parts can be reduced, deformation of the parts can be controlled, and precision of the parts can be guaranteed.