The invention discloses a control device for transverse mortar joints of a masonry wall and the levelness and flatness of the wall. The control device is fixed between an upper floor slab and a lowerfloor slab, tightly abuts against a structural column beside the masonry wall and comprises a rectangular vertical pipe, an infrared lamp which is vertically arranged is detachably arranged in the rectangular vertical pipe, the side, in the length direction of the rectangular vertical pipe, of the rectangular vertical pipe is provided with a plurality of light-transmitting holes with the central axes in the same straight line at equal intervals, the infrared lamp emits a plurality of parallel transverse mortar joint indication lines outwards through the light-transmitting holes after being electrified, the distance between every two vertical adjacent transverse mortar joint indication lines is the sum of the longitudinal height of one building block and the preset thickness of one transverse mortar joint. The control device for the transverse mortar joints of the masonry wall and the levelness and flatness of the wall has the dvantages of being simple in structure and convenient to install, and the operation of workers cannot be influenced.