The high plateaus in west China may provide suitable sites for astronomical observations with institute's middle-range telescopes and possibly with larger telescopes. Under China-Japan collaborations on site survey in west China, we have been conducted to search for good sites and monitored their characteristics for several years at Karasu (Xinjiang Uighur), Oma(Tibet), and Ali(Tibet). Recent results of our site survey show sites in west Tibet are revealed with high possibility for good astronomical observations. We present the characteristics at Oma, west Tibet, with its high sky clearance especially in winter, which is comparable to Mauna Kea, Hawaii. We present more possibility for astronomical observations at the westernmost site in Ali, close to Indian border.