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 is measured under various bending diameters, and it also be calculated theoretically. Beam quality factor M2 is measured by the means of knife edge for different bending of LMA fiber and the slope efficiency is measured separately. When bending diameters of 285 mm, 195 mm and 130 mm are used, the corresponding beam quality factors are 2.88, 1.82 and 1.67 with the slope efficiencies of 39%, 35% and 34% respectively. For the LMA multimode fiber used in the experiment, losses of different modes are calculated theoretically under various bending diameters.