The invention relates to a brake beam stretching anti-cracking device, which comprises a base, a positioning plate, and an adjustable cushion block, and is characterized in that: the base consists of two plates which are vertically butted; the middle of the vertical plate of the base is provided with a slotted hole; the horizontal plate of the base is provided with a bolt hole; the positioning plate is inserted into the slotted hole, and is fixed to one side end of the slotted hole; a hole for mounting the adjustable cushion block is reserved between the positioning plate and the other side end of the slotted hole; and the adjustable cushion block consists of a horizontal plate and a cushion block body connected to one end of the horizontal plate, the horizontal plate is inserted into the slotted hole and limited by the positioning plate, the surface of the cushion block body is a cambered surface, and the circle radius of the cambered surface is R 755mm. The brake beam stretching anti-cracking device has the advantages of strong generality, high flexibility, low price of used materials, good economy, convenient clamping and use, effective elimination of stretching cracks in the brake beam manufacturing process, and guarantee of product quality.