ITO thin films used in PTCDA/Si detector should be made at low temperature for low temperature resistance of substrate. ITO thin films were deposited at low temperature by RF magnetron sputtering. Properties of ITO thin films such as conductivity and transmission measured by 4 point probe and UV spectral photometry respectively. The results show that the sputtering pressure is an important parameter in the deposition of indium tin oxide（ITO） thin films, which affects the properties of ITO films. The optimized parameter for preparation of ITO thin films at low temperature are sputtering pressure 0.45 Pa, sputtering power 45W. Meanwhile, the post-annealing is not necessary.