The present invention discloses a screw gap detection device gap detection mechanism and a detection method thereof. The screw gap detection device gap detection mechanism comprises an upper support; an upper cylinder arranged on the upper support; an upper pneumatic gripper connected with a piston rod of the upper cylinder, wherein the upper cylinder can drive the upper pneumatic gripper to move up and down, and the upper pneumatic gripper can clamp a screw sleeve; a lower support; a lower pneumatic gripper arranged on the lower support and capable of clamping a screw; a displacement sensor arranged on the upper support and capable of inducing the displacement of the upper pneumatic gripper. The screw gap detection device gap detection mechanism and the detection method thereof can detect the gaps of the screw and the screw sleeve automatically, and are high in working efficiency and automation degree.