A plastic mould for a formed concrete shrinkage test piece comprises a plastic mould box, wherein an air inflation hole is arranged in the center position of a bottom board of the plastic mould box, the upper portions of two opposite side faces of the mould box are respectively provided with an opening, each opening is inserted with a movable plug-board, the lower edge of the opening extends outward to form a support edge, the upper portions of the other two opposite faces of the mould box are one support edge width wider than the power portions, the extra portion is provided with a slot in the vertical direction, a lower half circular groove is arranged downwards in the middle portion of the upper surface of the support edge, an upper half circular slot is arranged on a position of the lower surface of the movable plug-board corresponding to the lower half circular groove, two sides of the movable plug-board are respectively provided with a side lug, and the movable plug-board is provided with a vertical groove at a position close to each side lug. The plastic mould for the formed concrete shrinkage test piece is made of plastic, so that cost is low. The matching manner of inserting type enables the whole mould to be assembled and detached conveniently, shortens the time of detaching and assembling, improves efficiency, and guarantees integrity of the shrinkage test piece. The plastic mould for the formed concrete shrinkage test piece can be applied in the shrinkage test of the formed concrete.