Abstract: With reference to mudstone porosity microstructure research results of Chang-7 segment of Yanchang formation,by applying nuclear magnetic resonance(NMR)logging evaluation technology of pore structure,combined with petrography observation,the analysis on mudstone undercompaction porosity and pore microstructure characteristics has been carried out,and the applicability of the equilibrium depth method to restore the abnormal Yanchang formation pressure of Ordos basin has been discussed.The results show that the nuclear magnetic resonance(NMR)evaluation of pore structure,pore structure observation and quantitative analysis,the measured porosity does not support the existence of abnormal plateau intergranular pore and porosity in undercompaction of Chang-7 segment of Yanchang formation.The acoustic transit time deviated from the normal compaction trend curve,and it can't reflect the segment abnormal plateau intergranular pore and porosity,and the equilibrium depth method to calculate the maximum phase embedded depth of abnormal pressure is not applicable.