The invention discloses a top plate locating line-drawing device and method for a construction site. The top plate locating line-drawing device for the construction site includes a leg supporting rod,a line-drawing rod, a right angle dividing ruler and sliding blocks on the leg supporting rod, the line-drawing rod and the right angle dividing ruler; a leg supporting tine is arranged at one end ofthe leg supporting rod and a leg supporting rod scale is arranged on the leg supporting rod; one end of the line-drawing rod is hinged to the leg supporting rod and a clamping groove is formed in theother end of the line-drawing rod; the line-drawing rod is an adjustable telescopic rod and the bottom side of the right angle dividing ruler is fixed to the sliding block of the leg supporting rod;a dividing ruler of the right angle dividing ruler is vertical to the leg supporting rod and penetrates through the sliding block of the right angle dividing ruler; and the sliding block of the rightangle dividing ruler is hinged to the sliding block of the line-drawing rod. The top plate locating line-drawing device and top plate locating line-drawing method for the construction site has the beneficial effects that the top plate locating line-drawing device for the construction site is simple in structure, top plate locating line-drawing can be quickly carried out in the condition of takinga laser demarcation device for auxiliary means in a short time and little harm to eyes and working high above the ground is not needed, and labor is saved and potential safety hazard does not exist.