After introducing the temperature real-time measurement system using lasers InGaAs/I and pyroelectric detector LiTaO_3, this paper mainly discusses the effect and control on temperature measurement accuracy by reflection radiation and detector radiation itself. Four measures on improving temperature measurement accuracy are presented: The first is using water-cooled shelter plate and cooling the detector by water. The second is making the detector head the measurement surface as vertically as possible. The third is choosing suitable wavelength bandwidth. The fourth is making electrical compensation. Some necessary calculations and analyses are given Experimental results show that temperature measruement accuracy is suitable for requirement in the range of 400~1200 ℃ after taking these optimal measures.