The invention discloses a machined part positioning mechanism for a numerical control machining lathe. The machined part positioning mechanism comprises a rotary disc, a containing groove, a sliding body and a positioning and clamping structure; the containing groove is formed in the circle center position of one side of the rotary disc, first connecting springs are symmetrically arranged on the inner side wall of the containing groove in an integrally-formed mode, and an arc-shaped plate is arranged at the other ends of the first connecting springs in an integrally-formed and connected mode.According to the machined part positioning mechanism for the numerical control machining lathe, through the arrangement of the containing groove, the first connecting springs, the arc-shaped plate andthe sliding body, good positioning function is achieved on a machined workpiece, rapidly positioning and fixing the workpiece can be carried out, convenience is brought to workers, the working efficiency is improved; and through the arranged positioning and clamping structure, the firmness of workpiece positioning and fixing can be improved, looseness is not likely to be generated in the machining work, the fact that normal work is carried out is guaranteed, the machining quality is guaranteed, and then the work economic benefits are improved.