Experiment study of dynamics characteristic of D shape inner cladding Yb 3+ doped fiber laser is presented. The fiber laser in one mirror and two mirror cavity is pumped by a multi mode laser diodes. Self pulsing regimes are obtained in one mirror cavity. The Brillouin pulses appear with the increasing of pump power. The pulse duration is as short as 10 ns. The self pulses are suppressed in the two mirror cavity. In this case the stability of the laser is improved, and the threshold of the laser decreases.