The invention provides a forming mechanism for coiling or paving of a composite material prepreg tape. The mechanism comprises a pressure cylinder, a direction switching block, a pressure acting rod, a pushing rod, a pressing roller support, a pressing roller and a scrapping knife, wherein the pressure cylinder is mounted at one end of a cylinder fixing block, and the other end of the cylinder fixing block is connected with the direction switching block; meanwhile, a piston rod on the pressure cylinder passes through the cylinder fixing block and the direction switching block and then is connected with one end of the pressure acting rod; the other end of the pressure acting rod is connected to the top end of the pushing rod, and the bottom end of the pushing rod is connected with one end of the pressing roller support; the scrapping knife is mounted at the other end of the pressing roller support; the pressing roller support is hinged with the pressing roller. According to the forming mechanism, the forming direction of the composite material prepreg tap is realized according to the connection relation between the cylinder fixing block and the direction switching block.