Directional manipulation of infrasound has important application prospects in engineering sectors such as geological disaster early warning, underground resource exploration, and industrial non-destructive testing. Nevertheless, restricted by the extremely long wavelength of infrasound, conventional acoustic radiators require oversized dimensions to modulate sound fields, which has long blocked the practical deployment of infrasound technologies. Targeting the innovative application of microstructured advanced materials in cutting-edge infrasound acoustics, this paper proposes a cavity-coiled double-layer composite acoustic metamaterial with a cooperative regulation mechanism to achieve directional infrasound radiation. The cavity layer enables gradual impedance matching to reduce interfacial acoustic reflection and preprocess incident spherical infrasound into quasi-plane waves. In contrast, the coiled channels generate controllable phase differences via variable propagation lengths and construct phase gradients at the structure’s exit surface for directional beam forming. The single unit cell size is only one-tenth of the wavelength of 20 Hz infrasound, achieving subwavelength miniaturization. Key structural parameters, including unit dimensions, number of coiled layers, and source–structure distance, are optimized through finite-element simulations to improve directivity gain. A physical prototype is fabricated and tested in outdoor field experiments. Measured results verify that the proposed structure produces well-defined directional acoustic beams at 20 Hz with a half-power beamwidth of 74°, featuring concentrated acoustic energy along the principal radiation direction and effective side-lobe suppression. This study extends the application of microstructured metamaterial from conventional mid-to-high frequency acoustics to ultra-low-frequency infrasound, delivering a novel material solution for the next generation of compact, engineering-oriented infrasound equipment.