In present work, we demonstrate that when a transverse magnetic (TM) Gaussian beam is incident to a magnetic metamaterial (MM) slab, it can be completely absorbed at a particular direction, resulting in a unidirectional perfect absorption. The unidirectionality is due to the time reversal symmetry (TRS) breaking nature of the MM; while the perfect absorbing effect is explained by the multiple scattering theory and the effective medium theory. By tuning the magnitude and the orientation of the external magnetic field, the working frequency can be adjusted and the unidirectionality can be reversed. Accordingly, we can design tunable compact optical devices to achieve unidirectional perfect absorption.