A boundary control in two-dimensional is proposed for a distributedparameter flexible beam with unknown disturbance and varying tension to minimize the beam vibrations．Flexible beam is a typical infinite-dimensional distributed parameter systems，and its hybrid dynamic model is described in terms of partial differential equations (PDEs) and ordinary differential equations (ODEs)．To avoid control spillover and achieve vibration control in two-dimensional，the PD （Proportional Derivative）boundary controllers in longitudinal and lateral direction are designed respectively based on the original infinitedimensional PDEs model and Lyapunov's direct method to reduce the flexible vibrations．With the proposed PD boundary control，the real-time and robustness of control system are ensured because the proposed controller is simple and independent of system parameters．The uniform boundedness and closed-looped stability can be achieved by Lyapunov's direct method．Simulation results illustrate the effectiveness of the proposed boundary control．