Aiming at the repair needs of the underwater Ｒobotic MIG welding for nuclear fuel pool，a lightweighted and entirely-sealed wire feeder was developed． The overall lightweighting is achieved by means of aluminum alloy shell，glass steel panel and other devices; the double driving roller wire feeding mechanism is adopted，and the miniaturization of the device is realized through the optimized layout of the components like welding wire tray． The shell is connected with the compressed gas through a trachea to realize the self-adjustment of the pressure of the device with the change of water depth． To compensate the change of wire feeding speed，a digital driving control system based on AＲM is designed which adopted negative feedback control of armature voltage and high frequency chopping technology． The digital communication interface circuit based on CAN is used to realize the digital integration with the underwater robot． Test results of underwater welding at the level of 20 m depth show that the wire feeding device has the advantages of high shell strength，stable and uniform wire feeding，quick response and good adaptability，and thus meet the requirements of underwater welding repair．