A novel process for cracking olefins including contacting a hydrocarbon oil with a catalyst in a riser reactor having multiple reaction zones under cracking reaction conditions; separating reaction products and the catalyst; regenerating at least a part of spent catalyst obtained, contacting a part of the regenerated catalyst with the hydrocarbon in the first reaction zone; contacting the other part of the spent catalyst and/or regenerated catalyst in at least one reaction zone after the first reaction zone with the products obtained in previous reaction zones.