A fiber Bragg grating-based linear-cavity fiber laser is proposed and demonstrated experimentally. A single-mode fiber Bragg grating is used as a wavelength selector in the fundamental mode, and four few-mode fiber Bragg gratings are used to reflect LP01 mode, LP11 mode, LP21 mode and LP02 mode at the same wavelength. Different modes can be reflected at the same wavelength between a single-mode fiber Bragg grating and four few-mode fiber Bragg gratings to form four sub-linear-cavities. This fiber laser, which enables simultaneous lasing of LP01 mode, LP11 mode, LP21 mode and LP02 mode at the same wavelength, plays an important role in the field of mode-division multiplexing fiber-optic communications.