The utility model discloses a safety lock of a caliper spanner of a machine tool and relates to a safety lock used for placement of the caliper spanner of the machine tool. The safety lock of the caliper spanner of the machine tool mainly solves the problems that for most machine tools, workers install or dismantle a workpiece by screwing a chuck by means of a caliper spanner, due to the unprofessional operation that the machine tool is powered on to be started by an operator under the condition that the caliper spanner is not dismantled, the chuck rotates and the caliper spanner on the chuck is thrown out, injury to people and damage to articles caused by the caliper spanner which is thrown out, and production safety can not be guaranteed. The safety lock of the caliper spanner of the machine tool comprises a shell, wherein a through hole with a size matched with the size of an outer circle of the body of the caliper spanner is formed in the shell, an opening is formed in the wall of the through hole, a switch is further installed in the shell, a contact of the switch stretches into the through hole through the opening in the wall of the through hole, and a connecting line of the switch is used for being connected with a control circuit of the machine tool in series. The safety lock of the caliper spanner of the machine tool has the advantages that the accidents that people are injured and the articles are damaged due to the fact that the caliper spanner is thrown out from the chuck are avoided, production safety is guaranteed, the structure is simple, and manufacturing is easy.