Abstract: Atmospheric pressure plasma jet (APPJ) has the ability to emanate a kind of low-temperature plasma plume suitable for material surface modification, particularly for three-dimensional objects. While helium-fed APPJ can readily produce a diffuse plume ideal for uniform treatment, argon-fed APPJ typically forms a filamentary plume that causes localized surface effects and potential damages. Achieving a stable, enhanced diffuse plume in argon APPJ remains challenging. This work demonstrates the realization of a diffuse argon plume using a pulsed APPJ enhanced by an axial magnetic field. The magnetic field (0–470 mT) confines the radial diffusion of electrons via Lorentz force, extending streamer propagation distance and promoting reactive species production. Diagnostics confirm significant improvements in plume length, emission intensity, streamer propagation distance, and reactive species density for the diffuse argon plume.