In this paper, we demonstrate an all-fiber linearly polarized fiber laser oscillator. The single polarization of the oscillator is achieved through the careful designing of the active fiber coiling. The relationship between fiber coiling diameter and polarization extinction ratio and optical efficiency is studied, whose results lead to an optimized system. The thermal management of the oscillator is also refined, which allows the oscillator to reach a maximum output power of 44.1 W with an optical-to-optical efficiency of 57.9％. A high average polarization extinction ratio of 21.6 dB is achieved during a 2-hour stability test. The oscillator also owns a narrow 3-dB bandwidth of 0.1 nm, as well as near-diffraction-limit beam quality of M2～1.14.