Based on the Kirchhoff law, according to the relationships between various technical parameters (energy and wavelength of laser source, area of sensitive unit of detector, relative aperture of optical system, etc.) and main specifications (temperature resolving power, temperature measurement sensitivity, relative sensitivity and accuracy), an optimal laser source of the practical real-time temperature measurement system employing laser diode and LiTaO 3 pyroelectric detector is proposed. Experimental results of laser show that temperature measurement accuracy is suitable for requirements in the temperature range of 400℃～1200℃.