In this paper, the fiber laser with D-shaped inner cladding fiber is presented. The fiber laser has a second mirror which configuration is called two-mirror cavity to provide different feedback and to stabilize the output. The dynamics with different feedback 4%, 40%, 70% and 90%etc. are studied. In experiment, it obtained 2.32W output with 4% Fresnel reflection of the fiber. With different feedbacks it founds three thresholds, Pth is the laser threshold, pthB is for SBS (stimulated Brillouin scattering) in the fiber laser, and is for SRS (stimulated Raman scattering). The higher feedback level is, the lower threshold is. Also the PthB dynamics appear different characters with the increase of pump power. Under certain condition, the output is stable ns pulses. The pulses width has relationship with the feedback from the second mirror. The phenomena are analyzed quantitatively.