In this paper, we show the exact controllability of a micro beam with boundary bending moment at time T > 0, which gives a confirmative answer to the open problem proposed by P. Guzman and J. Zhu. The semi-group approach is adopted in investigation. The asymptotic spectral expression of the micro beam system is presented to verify an observability inequality for the dual system. By the duality principle, the exact controllability of the system is then established.