Based on the Kirchhoff law, a practical real-time temperature measurement system using laser diode and LiTaO 3 pyroelectric detector is developed. According to the relations between main specifications(temperature measurement resolving power, standard deviation and range) and main technical parameters of the instrument, such as laser energy and wavelength of emitting source, bandwidth of amplifier and relative aperture of optical system, the above technical parameters are optimized. Experimental results show that temperature measurement accuracy is better than 0.3% and temperature resolution is better than 0.4 K at 673～1473 K. They are both in accordance with the requirement.