Abstract: SEM test, mecury injection test and high pressure triaxial test are conducted to obtain the microscopic structure and deformation of natural sedimentary diatomaceous earth. Fractal characteristics of natural sedimentary diatomaceous earth and evolutions of pore structural characteristic parameters under different consolidated pressures are analyzed by image segmentation and optimal dividing threshold algorithm. The relationship between fractal dimension and isotropic consolidation is discussed. The results show that there are many pores in the diatomaceous earth which is strongly structural. The pore diameter distribution is mainly in the range of 0.1~1.0 μm. When consolidated pressure increases to yield pressure, pores whose diameters are larger than 0.1 μm are changing obviously. The number of large pores decreases with the increase of consolidated pressure, and the diatomaceous particles are destroyed and the pore structure is collapsed. The imaging characteristic of diatomaceous earth is analyzed, and then the gray threshold under different consolidated pressures is calculated by optimum dividing threshold algorithm. Based on the corresponding gray threshold, the grey images are then transformed into the binary image. The fractal characteristics of natural sedimentary diatomaceous earth under different consolidated pressures are studied. It is proposed that the binary images have obvious fractal characteristics and the fractal dimension increases with the consolidated pressure. Fractal dimension can not only represent the variation of micro structure but also represent the variation of void distribution of natural sedimentary diatomaceous earth.