Based on the basic law of mudstone compaction，this paper does a systematic research on the mudstone compaction characteristics in the west slope of Songliao Basin by using various logging data. The overpressure is quantitatively calculated and analyzed. The results show that the strata in the western uplift zone of the study area are basically in normal compaction state，while the Qingshankou and Nenjiang Formations in the Longhupao terrace and QijiaˉGulongkou sag show under compaction. The causes of difference in compaction in different areas are analyzed through comparison of the key parameters of compaction curves and in combination with real geoˉlogic data. On the basis of this，we quantitatively calculate the overpressure in the study area，analyze the structural features and plannar distribution of formation pressures，and predict the features of subsurface fluid migration and accumulation.