Geochemical analysis results of 30 source rock samples from Lishu fault depression in Songliao Basin show that samples are compositionally similar and represent a uniform organic facies.Differential distribution of steranes among the samples is due to rank,with vitrinite reflectances (Ro) ranging from 0.65 to 1.61％.In the maturity stage (Ro =0.65-1.20％),the absolute concentrations of steranes increase,which is affected by kerogen degradation,whereas the pyrolysis of high mature source (Ro =1.20-1.61％) show a decrease in the abundance of steranes.Simultaneously,the parameters of steranes vary greatly with maturity.Decrease of prognane/regular sterane value with the increase of maturity suggests that pregnane is not a product of regular steranes pyrolysis.The ratios of C27/C29 regular sterane gradually increase,while the value of C29-20S/(20S + 20R) and αββ/(αββ + ααα) decrease at high maturity stage,which is associated with the difference in the thermostability of steranes involved.This reversed trend can be used to determine the high-maturity stage of source rocks.Whereas the values of rearranged steranes/regular steranes in source rocks show an apparent positive correlation with maturity,it,therefore,appears to be particularly useful for maturity assessment at elevated levels.