Abstract: Junggar basin is a typical central massif type composite superposition basin, in which multiple cycle structu re formed various structure combination and sedi-mentary system and controlled oil and gas generation, migrat ion and accumulation. The studies on orga nic geochemist ry showed that there are sixsts of oil source rocks wit hin the basin, majorone is in Permian, the next in Middle and Lower Jurassic. Verticle mi-gration of oil and gas along fatjlts is rema rkable and formation of most reservoirs is related with this fact. Formed cond itions and distribution regulars of large oilfields indicated that sufficient oil and gas resou rces, better traps, favourable oil and gas migration direction, unim peded migration pathway, stable preser vation environment, effective caprock, and high quality reservoir bod y are importa nt geological factors, not a single. one can be omitted. It is forecasted that favourable area are Lunan slope zone, northwest margin slopem，Fudong slope zone, Mahuanticline, Da basong arch and south margin of Junggar basin.

Key words: Junggar basin, Large oil and gas field, Formed condition, Distribution, Forecasting