The invention discloses a submicron powder ultrasonic atomization grading device and an application thereof, and belongs to the field of powder grading. The ultrasonic atomization grading device comprises an ultrasonic atomization device, a solution inlet, a solution outlet, a nitrogen inlet and a nitrogen outlet; a liquid whistle dispersing device is arranged behind the solution inlet, the liquidwhistle dispersing device comprises a pipeline for installing a pore plate and a pipeline for installing a reed, and the two parts of pipelines are connected through flanges; and a silicon powder collecting device is arranged in front of the nitrogen outlet, a liquid level sensor and transducers are installed on the inner wall of a container of the ultrasonic atomization device, the number of thetransducers is 4-6, and the transducers are all installed at the same height. According to the ultrasonic atomization grading device, submicron silicon powder is graded by adopting an ultrasonic atomization grading mode, so that the problems that a conventional grading mode in the prior art is long in grading time, low in precision and complex in process are solved, and raw materials are subjected to dispersion treatment, so that the grading efficiency of the ultrasonic atomization grading is improved.