Abstract: Based on the Kirchhoff law,a practical temperature real-time measurement system using laser diode InGaAs/I and LiTaO3 pyroelectric detector is presented.By means of analyzing the relationships among resolving power of A/D converter,temperature measurement sensitivity of V(T)-T curve and temperature measurement range,16bite A/D converter for this instrument is determined.According to the relationships among temperature measurement accuracy,relative temperature measurement sensitivity of V(T)-T curve and waveleng ths,further optimal wavelength is discussed.Based on the relationships among resolving power of the detector and A/D converter and temperature sensitivity of V(T)-T curve,further optimal wavelength bandwidth is analyzed.Temperature measurement sensitivity of the instrument at 673K～1473K is given.Temperature measurement sensitivity is above 0.5K at lower temperatures and above 0.1K at higher temperatures at 673K～1473K after using optimal parameters.Temperature measurement inaccuracy at 673K～1473K exceeds 0.3%.