Abstract: Hydraulic permeability increase technology is currently one of the key techniques for gas prevention and control. However, existing methods still suffer from issues such as discontinuous decompression zones and complex construction processes. To further improve coal seam decompression and permeability increase, a novel method of axial plane slotting using in-seam jet cutting is proposed. First, a theoretical model for plane slotting was established. followed by an analysis of how surrounding rock pressure and jet slotting parameters influence the development morphology of pressure-relief fractures. This revealed the pressure-relief and permeability increase mechanism of the axial plane slotting technique along the coal seam, and optimized the axial plane slotting parameters. Field application tests were conducted for three technologies: pre-extraction through boreholes along the coal seam, annular slotting through boreholes to increase permeability, and axial plane slotting through jets to increase permeability. The advantages and disadvantages of the three technologies were compared. The research findings indicate: When the lateral pressure coefficient is 1 and the confining pressure increases from 18.75 MPa to 40 MPa, the fracture development height exhibits a linear upward trend. Below 18.75 MPa, non-through fracture zones exist, and the larger the lateral pressure coefficient approaches 1, the larger the de-pressurized fracture zone becomes. When the horizontal slot spacing is 1.25 m or less, the de-pressurized fracture zone achieves full connectivity. With vertical slot spacing below 5 m, fractures between two rows of slots can form a connected zone. However, when vertical spacing exceeds 5 m, fracture connectivity between slots becomes difficult. For coal seams thicker than approximately 4 m, two rows of slots can be constructed. Field tests indicate that compared to the following-strike drilling pre-extraction technique and longitudinal annular slotting for permeability increase, jet axial planar slotting increases gas extraction concentration by 0.27 and 0.5 times, boosts net gas extraction by 1.43 and 2.35 times, and reduces the time to achieve extraction targets to 48 days. This further validates the effectiveness of the jet axial planar slotting pressure relief and permeability increase technique.