The invention discloses a three-impeller type cotton straw fiber splitting machine; a motor is installed on a bracket; one end of a motor shaft is connected with the motor; the other end is connected with a main belt pulley; the main belt pulley is connected with a secondary belt pulley via a belt; the secondary belt pulley is connected with a small belt pulley via a belt; a big impeller is connected with a big impeller shaft; the big impeller shaft is connected with the secondary belt pulley; a small impeller is connected with a small impeller shaft; the small impeller shaft is connected with the small belt pulley; the big impeller and the small impeller are both arranged inside a processing room; a discharge port is arranged on one side of the processing room. In the three-impeller type cotton straw fiber splitting machine, the fiber can be disaggregated and splitted by the dispersing and cutting of the big and small impellers; the preparation efficiency is high; the fiber processing effect is good; an effective processing apparatus is provided for making fiber materials for bituminous pavement from the cotton straw; the waste of cotton straw resource and the environment pollution can be reduced; and farmers can be benefited.