During vacuum preloading treatment of dredged sludge, the non-filter membrane straw drainage body offers significant advantages, such as eliminating the need for filter membranes and resisting clogging, making it a promising solution for practical applications. However, the permeability characteristics and pore structure of the straw filter layer remain poorly understood, limiting its widespread adoption. This study investigates the permeability behavior and pore structure evolution of the non-filter membrane straw drainage body under vacuum preloading through laboratory permeability tests and CT scanning. Results show that the straw filter layer occupies 31.42% of the total volume, with fissure structures accounting for 14 times the volume of pore structures, forming a vertically and horizontally interconnected drainage network. The permeability performance of the non-filter membrane straw drainage body is superior to that of conventional geotextile filter membranes. The permeability coefficient of the non-filter membrane straw drainage body filtration system decreases rapidly and then stabilizes with increasing vacuum preloading time, ultimately reaching a stable value an order of magnitude higher than that of geotextiles used for clay filtration. Additionally, increasing the filter layer thickness and reducing the initial water content both lead to lower permeability coefficients. Under vacuum preloading, the structural transition of the straw filter layer—from a fissure-dominated to a pore-dominated structure—achieves a balance between soil retention and water permeability. These findings provide theoretical support for the engineering application of the non-filter membrane straw drainage body filtration systems in environmentally sustainable dredged sludge stabilization.