Bacterial sepsis is a lethal disease triggered by microbial pathogens. The blood pathogen load is a major contributor to both disease severity and mortality in patients with sepsis blood. Therefore, it is crucial to reduce the load of pathogens, in particular the drug-resistant pathogens. In this work, inspired by the crossflow filtration mechanism in suspension-feeding fish, we developed a biomimetic microcavity interface to mimic a porous gill-raker surface as a blood-cleansing dialyzer for sepsis therapy, which can rapidly, safely and efficiently clear bacteria from the fluidic blood. The microcavity interface consists of microcavity arrays, the innerface of which contains nanowire forests. By precisely controlling the pore size of the microcavity and directing the axial travel of the fluid, the bacteria can be isolated from the whole blood without disturbing any blood components or blocking the blood cell transportation. In addition, the three-dimensional nanowire forests assist in the formation of vortices with reduced blood flow velocity and increased resistance to bacterial deposition in situ. Functional modification is not required to recognize the bacteria specifically in our designed dialyzer. Moreover, the microcavity interface clears over 95% bacteria from a fluid blood sample without inducing protein adsorption or complement and platelet activation when contacting the fluid blood. The study supports this biomimetic microcavity interface to be a promising extracorporeal blood-cleansing device in clinical settings.