Large electric motor rotor casing tool and casing method

The invention discloses a large electric motor rotor casing tool and casing method which can help solve a problem that hidden danger of large accidents exists in conventional large motor rotor casingprocesses. The large electric motor rotor casing method comprises the following steps: a stator (3) lies horizontally on a stator support rack (2); a rotor carrying trolley (27) and a rotor follow-uptrolley (5) and a follow-up support rack (6) are respectively arranged on a guide rail (4) in movable manner; a rotor lies horizontally on the rotor carrying trolley (27), a driving electric motor (13) drives a lead screw nut (26) to rotate via a belt, and a lead screw (25) above a cantilever beam is driven to perform axial linear motion; as the lead screw (25) is arranged between a left top connection plate (23) and a right top connection plate (24) disposed on a top surface of an assembly guiding sleeve cylinder (10), the lead screw (25) is axially linearly moved to drive the assembly guiding sleeve cylinder (10) to