The output capability of large mode area (LMA) multimode fiber laser depends on the fiber bending. To study the relationship, the output capability of multimode fiber laser was measured under various bending diameters, and it was also theoretically calculated. Measured respectively were the beam quality factor M2, by means of knife edge for the different bending diameters of LMA fiber, and the slope efficiency. When the bending diameters 285, 195 and 130 mm were used, the corresponding beam quality factors were 2.88, 1.82 and 1.67 with the slope efficiency at 39%, 35% and 34%, respectively. In addition, for the LMA multimode fiber used in the experiment, losses of different modes were calculated theoretically under various bending diameters. The experimental results correspond to the calculated results.