Compared with master oscillator power amplifiers, fiber laser oscillators have the advantages of compact structure, low cost, strong anti-reflection light return capability, and good stability. With the development of fiber optic devices and processes, all-fiber laser oscillators achieve a near-diffraction limit output of 5 kW. As for the ytterbium-doped fiber laser oscillator, the research progress and problems faced by the space-coupled fiber oscillator and the all-fiber oscillator are introduced in detail. According to the nonlinear effects and mode instabilities that are the main limiting factors of high-power fiber laser oscillators, the technical approach to further increase the power of high-power fiber laser oscillators is discussed preliminarily, from the aspects of specially designed gain optical fibers and global oscillator optimization, in order to provide reference for the realization of single-mode fiber laser oscillators with 10 kW output.