The invention discloses a semi-automatic instrument lathe, and relates to the technical field of mechanical processing equipment. The semi-automatic instrument lathe comprises a control panel, a worktable, a case and a tool holder, wherein a clamping mechanism, comprising an elastic clamping sleeve, a bushing and a pulling rod workpiece, is arranged in the case; the tool holder provided with a turning tool is arranged on a transverse supporting plate which is arranged on a guide rail; the elastic clamping sleeve can slide relative to the bushing; the pulling rod is connected to the tail part of the left end of the elastic clamping sleeve; a cone section is arranged in an outer circle at the right end of the elastic clamping sleeve, and an inner hole fits the workpiece; gaps are uniformly distributed in the right end of the elastic clamping sleeve; a cone hole fitting the elastic clamping sleeve is formed in the right end of the inner hole of the bushing; the bushing is driven by a motor through a transmission part; the elastic clamping sleeve is pushed and pulled through a pulling rod which is connected to a translating mechanism, and the elastic clamping sleeve slides relative tothe bushing through the gaps, and thus the workpiece is clamped or released; the total length of the workpiece can be balanced and the chamfering processing of the workpiece can be realized through the turning tool on the tool holder. The semi-automatic instrument lathe has the advantages of being simple and compact in structure, and convenient to operate.