A device and a method of flattening recycled carbon fiber material are provided. A main body is provided with two flat plates at an upper and a lower positions corresponding to each other and an ultrasonic unit is disposed on each of the flat plates. While in use, recycled carbon fiber material is placed at the lower flat plate and then at least one ultrasonic probe of the ultrasonic unit is driven to work and vibrate the recycled carbon fiber material into a flat and thin state. After the flattened recycled carbon fiber material being pressurized to form products required, the product has flat and smooth surfaces with special textures. A thickness of the product can be controlled and the product can be thinned according to users' needs, without surface treatment such as grinding, polishing, etc. Thereby production cost is reduced and yield rate of the products is improved.