The invention discloses a radian copying drawing device for a three-way pipe. The device comprises a drawing board support, wherein a drawing board is arranged at the upper side of the drawing board support; telescopic supporting legs are connected to the lower side of the drawing board support; a quadrate connecting rod assembly is connected to the drawing board support and can slide along the drawing board support; the quadrate connecting rod assembly comprises a handle sliding block which can slide along the drawing board support; a quadrate connecting rod is inserted into the handle sliding block and can slide up and down in the handle sliding block; a Z-shaped pencil holder which is connected to a pencil is connected to the upper end of the quadrate connecting rod, and the tip of thepencil is in contact with the drawing board; a positioning block is arranged at the lower part of the quadrate connecting rod; a part, positioned between the positioning block and the handle sliding block, of the quadrate connecting rod is sleeved with a first spring; a wheel which can roll on the outer contour of the three-way pipe is connected to the bottom part of the quadrate connecting rod. The device is simple in structure, convenient to use, high in working efficiency, and capable of drawing arc-shaped outer contour curves in any angle on a branched pipe and a main pipe of the three-waypipe.