The invention discloses a gear-fixed cutting structure composite drill bit and belongs to the boring field. The drill bit comprises a drill bit body, as well as a gear and a fixed cutting structure which are arranged on the former, wherein the gear is in rotational connection with the drill bit body through a bearing structure; wide inserted teeth are embedded into the gear, the absolute value of the deflection angle Alpha of the top of each inserted tooth is larger than or equal to 70 degrees and smaller than or equal to 90 degrees, each inserted tooth is mushroom-type, and the width of the top of each wide inserted tooth is not less than 80 percent of the horizontal length of each wide inserted tooth; and the fixed cutting structure comprises a plurality of fixed cutting teeth. The composite drill bit can improve the rock breaking efficiency and is prolonged in service life.