Abstract: While ultrasonic technology offers advantages of non-invasiveness and precise focusing for brain disease treatment and neuromodulation, the high acoustic impedance of the skull causes significant energy loss and wavefront distortion, limiting its transcranial transmission efficiency, and conventional optimization approaches still struggle to overcome this physical limitation. To address this challenge, this study proposes a functional double-negative acoustic metamaterial, designed based on transformation acoustics theory, comprising coupled silicon nitride membranes and Helmholtz resonators. The metamaterial exhibits simultaneous negative effective density and negative bulk modulus in the frequency range of 0.30–1.38 MHz. Theoretical analysis and numerical simulations reveal that the proposed metamaterial can effectively suppress acoustic reflections at the skull interface and significantly enhance transmission efficiency at around 1.0 MHz. Furthermore, a quasi-one-dimensional array composed of these unit cells demonstrates robust performance in various transcranial focusing scenarios, including single-point focusing, multi-point focusing, and self-accelerating beam formation, validating its potential application value in complex acoustic field manipulation.