Abstract: The typical structure of the rotary fixture for the horizontal machining center turntable is to configure the turntable, tailstock, and clamp on the workbench of the horizontal machining center, thereby forming a cradle type turntable. This method can centralize the machining process, further improve the machining quality and efficiency of the parts. Based on the analysis of the composition type of the cradle type rotary fixture, the positioning pin connection is taken as the research object. By discussing several parallel relationships between the positioning pin connection, the rotary axis of the turntable, and the machine coordinate system, a mathematical model is established, and practical problems encountered in the production process are solved through examples.