The invention discloses an unstressed flattening device and method for cylindrical bamboo wood with bamboo green and tabasheer. The device structurally comprises a motor, a motor base, a protective cover, a knife roll, a flattening roll, an air cylinder, a flattering roll bearing sliding base, a sliding groove, a limiting bolt, a knife roll bearing fixing base, a chain and a gearbox. The flattening method comprises the steps of (1) heating the bamboo wood to reach the glass-transition temperature, (2) rapidly flattening the bamboo wood in an unstressed mode, (3) planing the bamboo green, (4) planing the tabasheer with the fixed thickness, and (5) conducting drying through overlapping and stacking in a tabasheer face-to-face mode or pressure drying. The unstressed flattening device and method for the cylindrical bamboo wood with the bamboo green and the tabasheer have the advantages that only one pair of rolls, namely the upper flattening roll and the lower knife roll are needed, the structure is simple, maintenance is convenient, operation is easy, the device and method can be suitable for flattening bamboo cylinders with different diameters, and the flattening effect is good; flattening of the heated bamboo cylinders in a heating tank is rapidly finished within 3 min to 5 min, fixed-thickness planing is conducted, most cracks of the tabasheer face are planed away when the tabasheer is planed, the tabasheer is in the adhesive face when finished products are formed, and the appearance and the strength are not affected.