Nano-TiO₂particles were modified respectively by silane coupling agent KH570 and KH171 with different chain length. The influence of KH570 and KH171 on the graft modifying effect of Nano-TiO₂was studied by FT-IR, TG, TEM techniques . The results show that the organic chain length of silane coupling agent can produce space steric hindrance effect . It plays a key role on modification nanometer particles. TEM show that dispersion effect on modifying nano-TiO₂by long-chain silane coupling agent( KH570 ) is much better. TG and wettability experiments show conent of long-chain silane coupling agent KH570 is 10 % , the coupling agent grafting rate and water contact angle is maximum, respectively 8 . 05 % and 76 . 6 ^o ; FT-IR show that long-chain KH570 bond strength is much stronger than KH171 .