An apparatus for testing temperature includes a plurality of thermocouples, a plurality of relays, a ground circuit, a compensation circuit, a power supply circuit, a switch circuit, and an MPU. The thermo-couples samples temperatures at different locations in a CNC machine, each thermo-couple is connected to a corresponding relay and selectively connected to the switch circuit by turning on or off the corresponding relay, the compensation circuit includes a cold junction compensator and a first relay, the ground circuit includes a ground terminal and a second relay, the power circuit includes a power supply and a third relay. The first, second, and third relays selectively turn on or off to connect the cold junction compensator, the ground terminal, or the power supply to the switch circuit. The switch circuit includes a capacitor and a fourth relay, the fourth relay is selectively connected the MPU, the ground circuit, the compensation circuit, or the power supply circuit to the capacitor, the MPU obtains voltage at the capacitor, and converting the voltage to a temperature signal.