The invention relates to a math teaching aid, which is good in drawing effect. A first housing is transversely and slidably connected with a first pull bar; the first pull bar is fixedly connected with a first double-face toothed bar; the two sides of the first double-face toothed bar are engaged with a first gear and a second gear respectively; the first gear is fixedly connected with a first connecting rod; and the second gear is fixedly connected with a first mark post. A second housing is transversely and slidably connected with a second pull bar; the second pull bar is fixedly connected with a second double-face toothed bar; the two sides of the second double-face toothed bar are engaged with a third gear and a fourth gear, which are rotatably arranged on the second housing, respectively; the third gear is fixedly connected with a second connecting rod; the fourth gear is fixedly connected with a second mark post; one end, away from the second gear, of the second connecting rod is fixedly connected with a telescoping rod; and the other end of the telescoping rod is fixedly connected with the end, away from the first gear, of the first connecting rod. The math teaching aid is high in precision and good in efficiency, can directly find the incenter of a triangle without making an auxiliary line, and meanwhile, can directly know the angles of the triangle.