Abstract: According to the molding requirements of plastic part for a bent pipe joint of pump pipe, a single-cavity single point gate injection mould was designed, The demoulding of the inner product in the cavity was divided into two cases, i.e. the demoulding of the outer wall and the demoulding of the inner wall. Three conventional demoulding mechanisms was used for the demoulding of the outer wall, whereas a demoulding mechanism of complex bend pipe was adopted for the inner wall. The demoulding mechanism structure consists of a side core pulling mechanism, a special cylinder driving and oblique core pulling off module mechanism with a telescopic sliding block, and a variable form rod pushing mechanism. The design of the mechanism of the core pulling out of the mold with a telescopic sliding block of the cylinder drive was especially carried out. The inner core of the pipe was arranged skillfully by a linear core pulling method. Such a design could avoid the problems of complex mechanism design and difficult movement control caused by the traditional rotary core pulling method in the bend pipe section of the inner wall. This design could also save the size of die holder and reduced the cost of mould manufacture. The reasonable layout of die structure could provide a useful reference for the similar products.