Abstract: According to the structural characteristics of plastic parts, a simplified three-plate die with double parting surface and four-point gate was designed. On the basis of optimizing the ejection mode of plastic parts and optimizing the gating system of plastic parts with CAE, the mold cavity layout adopts one mold and one cavity. To solve the problem of difficult demoulding of plastic parts, a four-sided core-pulling compound mechanism was designed to realize automatic demoulding of plastic parts. With the opening action of the template, a compound four-sided core-pulling mechanism was designed to realize complete demoulding of plastic parts. When demoulding, the core-pulling of the core insert is separated from the plastic part by the opening action of the moving template and the fixed template under the ejection of the pneumatic ejection. At the same time, the core-pulling of the vertical core-pulling insert is driven by the slider of the central tunnel driven by the oblique T-groove, and then the side core-pulling of the vertical core-pulling insert is carried out downward by four sliders driven by two cylinders. At the same time, the plastic part is also assisted by the pneumatic ejection. When the part is pulled out, the plastic part is left on four downward core-pulling sliders. In the following four downward side core-pulling sliders, because the four sliders are driven by their respective oblique guide pillars, the side core-pulling is done synchronously, and the plastic part is automatically separated from the four side sliders, thus realizing the automatic demoulding of the plastic part. The mechanism design is ingenious and the die mechanism design is reasonable, which can provide useful reference for the die design of similar plastic parts.