In order to study the microstrcutrue of the lacustrine soft clay under different consolidation pressures, SEM and quantitative analysis of consolidation samples were carried out through GDS consolidation undrained tests with different consolidation pressures. A different consolidation stress of 50 kpa, 100 kpa, 200 kpa, 400 kpa, 800 kpa, 1600 kpa and stress rate of 0.01 mm/min were used in this GDS test. The back pressure 10 kpa was unchanged, with different axial compression P1 (60 kpa, 110 kpa, 210 kpa, 410 kpa, 810 kpa, 1610 kpa) pressure of cylinder (76.2 mm diameter and 20 mm height) specimen was lasted 24 hours, while microstructure parameters of the specimen were obtained by using SEM image and the PCAS(Particles and Cracks Analysis System)s. The results show that the boundary points of primary consolidation and secondary consolidation of lacustrine soft clay are not obvious at low consolidation pressure. The consolidation pressure increases, the slope of the fractal dimension of porosity rainfall curve is larger and the reduction rate is faster, and the probability entropy is above 0.96. When the consolidation pressure is larger than 400 kPa, with the increase of the consolidation pressure, the slope of the fractal dimension value change curve of porosity slows down. The average shape coefficient increases faster when the consolidation pressure is less than 400 kPa, while the fractal dimension decreases faster. The correlation coefficients between consolidation pressure and fractal dimension value of porosity, probability entropy, average shape coefficient and fractal dimension are all greater than 0.81, showing a high correlation.