Abstract: Baimiao gas field is half of rollover anticline controlled by Lanliao fault and it is a combination trap not only controlled by structure, but also by lithology.The Baimiao gas field is found in 1980.And the main formations are down of the Sha-2, upside of the Sha-3, middle of the Sha-3 and down of the Sha-3.During the past twenty years, we have mastered the structure characteristics by exploring and researching.And seeking the lithological traps would be geological studying drection, instead of seeking structural trap with going deep into rolling development.The ex ploration indicates that the upside of the Sha-3 is the main producing formation.The relation between sedimentary environment and the distribution of sandst one and the characteristics of lay-aside are discussed emphatically in this paper by researching sediment ary environment of upside of the Sha-3 in Baimiao gas field.It gives the advantageous facies tract of oil and gas gathering.It is very meaning for the next exploration.