The invention discloses a device and a method for measuring the verticality of a cross shaft. The device comprises a base plate, a dial indicator bracket and a dial indicator, wherein fixed grooves which are mutually vertical, crossed and communicated are formed on the base plate; two V-shaped seats which are arranged linearly are arranged in one of the fixed grooves; a right-angle block is arranged in the other fixed groove; V-shaped positioning surfaces are arranged on the V-shaped seats; a right-angle positioning surface is arranged on the right-angle block; and the dial indicator is clamped on the dial indicator bracket and positioned on an opposite side of the right-angle block. The method comprises an adjusting step and a measuring step. In the adjusting step, a reading of the dial indicator is at a relative middle reading position. In the measuring step, contacts of the dial indicator are contacted with surfaces and outermost points of journals of a workpiece, the readings of the dial indicator of the two adjacent journals are respectively acquired by rotating the cross shaft 90 DEG, and a difference between the indications is a verticality error value of the measured workpiece.