A filtration separation method for waste resin containing highly radioactive uranium powder and device thereof is mainly used for the waste resin after water treatment process in a nuclear facility. The uranium powder contained in the waste resin is highly radioactive. Thus, prior to the treatment of the waste resin, it is necessary to filter and separate the highly radioactive uranium powder to reduce the radioactivity. It is to put the uranium powder containing waste resin into an underwater holding tank and withdraw the waste resin by an underwater pump into a uranium powder filtration box. Then the uranium powder filtration box is lifted by a hoist to move to an underwater ultrasonic cleaner. High-pressure water flushing is applied and followed by underwater ultrasonic cleaning. Then the cleaning water (containing precipitated uranium powder) from the ultrasonic cleaner is drained to uranium powder collection device. If the radioactivity of the waste resin is still high, high-pressure cleaning by water nozzle flushing and ultrasonic cleaning are applied several times until the radioactivity of the waste resin is lowered to the treatment standard and converted to low-radioactivity waste for further treatment.