We report here the first watt-level efficient single-pass 1.54 μm fiber gas Raman source by methane-filled hollow-core fiber operating at atmospheric pressure. Pumped with a high-power MOPA (master oscillator power amplifier) structure Q-switched 1.06 μm pulsed solid-state laser, efficient 1.54 μm Stokes wave is generated in a single-pass configuration by vibrational stimulated Raman scattering of methane molecules. With an experimentally optimized fiber length of 3.2 m, we get a 1543.9 nm Stokes wave operating at atmospheric pressure with a record average power of ~0.83 W, which is about 12 times higher than the similar experiment previously reported, and the corresponding power conversion efficiency is about 45%. Operating at atmospheric pressure makes it more convenient in future applications.