The object of the present invention is to provide a method for growing a large-size crystal by laser assisted heating and a dedicated device. The device comprises a laser core heating device, a xenon lamp surface heating device, a base, a vacuum cavity and etc. When a crystal is prepared, seeding and crystal growing are implemented by a xenon lamp-laser synergetic heating mode. According to the present invention, the structure and functions of the dedicated device are designed to introduce, at the center of a float melting zone, a laser heating source having high precision and strong controllability, so that a composite heating mode with xenon lamp surface heating and laser core heating is formed; and combined with the control of process, the method and the device solve the difficulty in growing a large-size test crystal bar and enable the growth of the crystal bar having a diameter up to 35 mm so as to facilitate engineering uses.