The invention discloses a helicopter transverse butt joint assembly angle steel tower rapid tightening device and a tower assembly method thereof, and relates to the field of overhead power transmission line construction. A helicopter assembles an overhead transmission line angle steel tower, and when the helicopter hoists an angle steel tower cross arm, as the hovering time for hoisting of the helicopter is limited, how to shorten the hovering operation time of the helicopter and how to quickly realize the in-place of the cross arm become difficult points. The device comprises a screw rod body, a stopping cantilever rotatably connected to the left end of the screw rod, a round nut screwed in from the right end of the screw rod and provided with a hand crank; when the cross arm is hoistedby the helicopter, the rapid tightening device is inserted into a cross arm main material bolt hole and an iron tower body main material bolt hole, then the stopping cantilever is pulled up by 90 degrees, and the hand crank is rotated to tighten the stopping cantilever; rapid positioning of the iron tower cross arm on the iron tower body is conveniently achieved, and the helicopter hovering operation time can be effectively shortened.