The invention relates to a positioning and assembling die for a ceramic shell of a vacuum switch tube. The positioning and assembling die comprises a supporting plate, a placement sleeve, clamping devices, a lifting plate, a positioning air cylinder and an alignment device, wherein the placement sleeve is arranged on the top of the supporting plate, and the left end and the right end of the placement sleeve are provided with the clamping devices respectively; the alignment device is positioned above the placement sleeve; the top of the alignment device is connected with the lower end of the positioning air cylinder; the lifting plate is installed on the upper end of the positioning air cylinder, and mounting holes are uniformly formed in the lifting plate; and the alignment device comprises an alignment clamping sleeve, a locking clamping jaw, a buffer spring, an adjusting column, a clamping-pressing column, a clamping-pressing spring, a laminating plate, a pushing column and a pushingspring. According to the positioning and assembling die, the problems can be solved as follows: the welding effect of the switch tube is poor due to the fact that a certain error exists in manual operation in the prior art, a three-jaw chuck easily causes damage to the ceramic shell and the three-jaw chuck cannot be attached to the appearance of the ceramic shell when the ceramic shell is lockedby the three-jaw chuck.