Based on the analytical data of GC/MS and GC/MS/MS for saturated fractions of over 40 different lithofacies source rocks and oils, the biomarker compositions in various depositional facies of Oligocene source rocks in Yacheng region, Qiongdongnan Basin, were characterized, and the oil-source correlation with a new viewpoint for Yacheng oil & gas field was intensively made. The results indicated that the coals and carbonaceous mudstones in coastal plain-swamp facies show a pronounced pristane predominance in isoprenoids(Pr/Ph>5.0), low molecular weight compound dominance in tricyclic terpanes(C19/C23>3.0), low amount of steranes(hopanes/steranes >5.0)and dominant C29 in steranes(>60%), indicating a predominantly terrigenous organic source and deposition in an oxic environment. The shallow marine mudstones display Pr/Ph ratios mostly in 1.0~2.5, indicative of subanoxic-oxic condition, and have a maximum peak at C21 or C23 in tricyclic terpanes and a "V" shaped modal in C27~C29 sterane distribution, suggesting a mixing input of terrigenous and aquatic organic matter. Oleanane and bicadinane used usually as terrigenous indicators are in low content in all the coaly rock samples, but commonly enriched in the mudstones, reflecting a special character for depositional organic matter in the nearshore marine environment. Therefore, the abundance of oleanane and bicadinane in the sediment of offshore basin could not be used as proportion for land plant input to overall organic matter, rather may be act as a facies-related indicator. According to the geochemical correlation by biomarkers with source rocks, the major oils in Yacheng oil and gas fields are believed to have a multiplex biomarker composition with coal and mudstone source characteristics, and be the mixed oils derived from various depositional facies of Oligocene source rocks.