The invention relates to a longitudinal folding device of a quilt folding machine, and belongs to the technical field of packaging machines. The quilt folding machine comprises a quilt tiling guiding-in mechanism, the longitudinal folding device comprises a front longitudinal quilt folding mechanism and a back longitudinal quilt folding mechanism, and the longitudinal folding device is characterized in that the back longitudinal quilt folding mechanism comprises a back longitudinal quilt folding rack, a back longitudinal quilt folding driven roller, a back longitudinal quilt folding driving roller, a back longitudinal quilt folding conveying belt, a back longitudinal quilt folding shaft, a back longitudinal quilt folding rod base, a back longitudinal quilt folding rod and a pair of back longitudinal quilt folding shaft power transmission devices; the front longitudinal quilt folding mechanism comprises a front longitudinal quilt folding rack, a front longitudinal quilt folding driven roller, a front longitudinal quilt folding driving roller, a front longitudinal quilt folding conveying belt, a front longitudinal quilt folding shaft, a front longitudinal quilt folding rod base, a front longitudinal quilt folding rod and a pair of front longitudinal quilt folding shaft power transmission devices. Opposite folding of the two sides of a quilt guided in by the quilt tiling guiding-in mechanism in the length direction is achieved through the front longitudinal quilt folding mechanism and the back longitudinal quilt folding mechanism, a foundation is laid for transverse folding of the follow-up working positions, operating strength is relieved, and the regularized packaging requirement is met.