The invention discloses a method for improving top coal cavability of fully mechanized caving faces by utilizing controllable source microwave radiation, and aims to solve the problem of coal loss caused by difficulty in hard top coal falling in the coal discharging process. According to the method, the selective and integral heating characteristics of microwave on all mineral components in the coal body are utilized to generate thermal stress, the coal body structure damage and thermal cracking are caused, the fracture development degree of the hard top coal is improved, the top coal strengthis reduced, and the purpose of improving the top coal cavability is achieved. The method is safe to use, the equipment can be recycled, the stoping disturbance to the caving faces is small, and the top coal caving effect is good.