///The shale within Chang 7 Member of Yanchang Formation in Triassic is an important source rock of Mesozoic reservoirs in Ordos Basin. The paleo-pressure in the period of accumulation plays a vital role for the hydrocarbon migration, and the changes of paleo-porosity represent the characteristics of the paleo-pressure evolution. Through analyzing the characteristics of present shale compaction profiles, there is an exponent relationship between the porosity increment and the maximum depth of undercompacted shale within Chang 7 Member. Then by using this relationship, the increment of shale porosity in the period of accumulation can be extrapolated and by combining the porosity of normal compaction trend, the total porosity of undercompacted shale within Chang 7 Member in the period of accumulation can be restored effectively.