The invention provides a catalytic cracking fractional and divisional transformation method and device for heavy oil. The method comprises the following steps of: classifying heavy oil raw materials into a high grade catalytic raw material and an ungraded catalytic raw material according to the difference between reaction properties, wherein a riser reactor is taken as the reaction area of the high grade catalytic raw material, and a combined reactor consisting of a turbulent bed or a fast bed and a conveying bed is taken as the reaction area of the ungraded catalytic raw material; undergoing a reaction under respectively optimized process conditions of low-dose oil contact temperature difference and high-dose oil ratio; separating reacted oil gas from a catalyst; leading the oil gas out of a reaction system; and introducing the catalyst into a catalyst regenerator for scorching and regenerating. The invention also provides a device for implementing the catalytic cracking fractional and divisional transformation method. In the method, malignant adsorption competition between the ungraded raw material and the high grade raw material in the conventional riser reactor and retardation on the reactions are effectively avoided, the problem of insufficient reaction deepness of the ungraded raw material is solved, and the yields of clean oil and liquid are remarkably increased.