To investigate the permeability of sludge solidified soil prepared using a self-developed water glass-based curing agent, the microstructure and pore size distribution characteristics of the soil were analyzed using scanning electron microscopy (SEM) and mercury intrusion porosimetry (MIP) with varying amounts of curing agent. Based on the effective porosity theory, a one-dimensional permeation differential equation was established, and a constant head permeability test scheme for fine-grained soil was proposed and applied to the permeability testing of the solidified soil. Through back pressure saturation and unloading tests, the relationship between the effective porosity rate increment and the pore water pressure function was established, and the permeability parameters of the soil were obtained through constant head permeability testing and numerical calculations. The permeability parameters of the solidified soil were studied with varying curing agent content. The results showed that with increasing amounts of curing agent, both the particle structure and porosity rate of the solidified soil increased. The initial effective porosity rate and starting hydraulic gradient of the solidified soil decreased monotonically, while the absolute effective permeability coefficient initially decreased and then increased, reaching a minimum value at a curing agent ratio of 7%.