A device for expanding spacing between spinous processes includes a first supporter, a second supporter and a pin. The first supporter includes a first protrusion, a second protrusion opposing the first protrusion, and a first concave portion formed between the first protrusion and the second protrusion for supporting one spinous process. The second supporter includes a third protrusion, a fourth protrusion opposing the third protrusion, and a second concave portion formed between the third protrusion and the fourth protrusion for supporting another spinous process. The pin pivots the first supporter to the second supporter so as to provide the device an expansion state and a close state for removal and installation between two spinous processes. In addition, a method for expanding spacing between spinous processes is also provided.