Abstract: To investigate the influences of abnormal fluid pressure on structural deformation in the northeastern Sichuan basin, on the basis of drilling and logging data obtained from 40 wells in the study area, the paper uses equivalent depth method to calculate fluid pressure in the shale section and corrects the pressure by combining with the actual measured fluid pressure to characterize the characteristics of the overpressure development in the study area and to match the variations of the fluid pressure with depth. The pore-fluid pressure ratio of different detachment layers in the northeastern Sichuan basin are calculated. The calculated pore-fluid pressure ratio is 0.38~0.72 for the gypsum-salt detachment layer in the Lower Triassic Jialingjiang formation, 0.48~0.78 for the shale detachment layer in the Lower Silurian Longmaxi formation, 0.61~0.87 for the gypsum-salt detachment layer in the Lower Cambrian Longwangmiao formation and 0.71~0.84 in the basement detachment layer, showing a feature of “lower in the east and higher in the west”. The pore-fluid pressure ratio of each detachment layer is used to obtain effective friction coefficient and the calculated effective friction coefficient of each detachment layer is 0.170~0.530, 0.130~0.320, 0.110~0.330 and 0.090~0.180 for Jialingjiang formation, Longmaxi formation, Longwangmiao formation and basement, respectively. Based on the through-well seismic profile interpretation, the intensity of the basement detachment layer is calculated as 0.060~0.110 by using structural wedge-related theories. Comparing the intensity with the effective friction coefficient, it is found that they are identical with each other, which can prove that the calculated effective friction coefficient of the basement detachment layer is reliable. When the fluid overpressure is not developed in the study area, the effective friction coefficient of the basement detachment layer should be 0.372~0.527, which indicates that the widely-developed fluid overpressure in the study area results in the reduction of the effective friction coefficient of the basement detachment layer by 79.1%~83.9%, indicating that the tectonic stress needed by shear action along the basement detachment layer significantly decreases