With the use of large-mode-area (LMA) double clad fiber, output powers of a single fiber laser increase dramatically. However, it makes the laser operate with high-order modes and the beam quality degrades at the same time. In this paper, fiber tapering is introduced to control high order modes of a LMA fiber laser, which has a 43 μm core with 0.08 NA. And a 20 mm length tapered zone is employed, 10 mm in front of the output end. And the minimum of the core diameter of the tapered zone is 9 μm. When the launched pump power is 119.1 W, 56.4 W single mode output can be obtained. On the basis of the experiment, thermodynamic characteristics of the tapered fiber laser are calculated theoretically. The experimental results are in agreement with the calculated results. And it offers a reference for achieving higher single mode fiber laser and its cooling scheme.