The temperature greatly influences the characteristics of laser diode. If a stable output wavelength is required, the temperature of the laser diode must be maintained a constant level. In this paper, we use the operation amplifier with high S/N, a normal temperature sensor with negative temperature modulus, and a semiconductor cooler as temperature control instrument, and we succeed in inventing a high precision temperature instrument which is used in the semiconductor diode temperature control, the precision of the controlled temperature is ±0.03℃.