The invention provides an improved leakproof structure for a building outdoor floor deformation joint, and relates to the technical field of building construction. The problems that gaps are prone tobeing left after assembly, the airtightness is poor, the phenomenon of water inlet possibly appears, the building quality is affected, assembly is inconvenient, and the function of quick dismounting is not achieved are solved, the improved leakproof structure includes bottom plates, the outer sides of the bottom plates are movably provided with sliding plates through threaded connection, the sliding plates are externally provided with housings in a clamped mode, a plurality of sets of damping devices are arranged between the two sets of the bottom plates, the surfaces of the two sets of the bottom plates can be sealed by arranging the sliding plates, the sliding plates can be matched with clamp pieces to move horizontally in T-shaped long grooves, and seal with a silicone strip during moving, the waterproofness of the surfaces of the bottom plates is ensured, and meanwhile, the damping devices can be arranged in a restricted mode by the sliding plates.