The output characteristic of hundred-micron core diameter fiber laser and its mode control technique are researched. In theory, feasibility of which using winding to control the modes of hundred-micron core diameter fiber laser is analyzed. In experiment, output modes of hundred-micron core diameter fiber laser are controled by the hole in the laser cavity, and the effects to beam quality are researched with holes of different diameters.When there is no hole in the laser cavity, the beam quality factors M2 are 4.67 and 4.60 in x and y direction. After adding 2 mm diameter holes in the cavity, the beam quality factors M2 are 1.96 and 2.01 in x and y direction.The beam quality is improved remarkably by the holes.