A linear-cavity all-fiber-based ultra short pulse laser system is provided. The all-fiber-based ultra short pulse laser system includes a pulse pump light source, a gain fiber, a first fiber signal pump combining unit, a broadband optical isolator, a fiber saturable absorber, an assistant light source, a second fiber signal pump combining unit, and a light coupling output. A broadband amplified spontaneous emission, emitted by the first fiber signal pump combining unit, which is connected to the pulse pump light source and the gain fiber, passes through the broadband optical isolator. The second fiber signal pump combining unit is connected to the assistant light source and the fiber saturable absorber. An ASE signal actively provides passive mode locking of the cavity, and the light coupling output partially outputs the laser. A dispersion fiber controls the temporal width.