TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred Method: The reaction in first reaction area I is carried out at 520-650 degrees C for 0.5-1.5 s and at agent/oil ratio of 7-12. The reaction in second reaction area II is carried out at 500-580 degrees C for 1-2 s and at agent/oil ratio of 8-15. The reaction in fluid bed reactor is carried out at 510-560 degrees C and weight hourly space velocity of 3-30hour. The reaction in second riser reactor is carried out at 520-560 degrees C. The atomized vapor of heavy material fed to first riser reactor is 2-50 preferably 5-15 wt.% of material feeding quantity, and reaction pressure is 0.15-0.35 MPa. The atomized vapor of heavy material fed to second riser reactor is 5-30 preferably 10-20 wt.% of material feeding quantity. The atomized vapor of C4 hydrocarbon is 10-40 preferably 15-25 wt.% of the material feeding quantity of C4 hydrocarbon. The reaction pressure of fluid bed reactor is 0.15-0.30 MPa. The agent/oil ratio of catalyst to cracking heavy oil in second riser reactor is 1-30 preferably 5-20. The weight hourly space velocity of cracking heavy oil in fluid bed reactor is 1-20 preferably 3-15/hour. The weight ratio of cracking heavy oil led to second riser reactor and fluid bed reactor to heavy material led to first riser reactor is (0.05-0.30):1, and normal-pressure distillation range of cracking heavy oil is 330-550 degrees C. The cracking heavy oil is led to fluid bed reactor. The weight ratio of light material in second riser reactor to heavy material led to first riser reactor is (0.05-0.20):1. The weight ratio of C4 hydrocarbon to gasoline fraction is (0-2):1. The stripped steam is led to bottom of fluid bed reactor, and separated carbon deposit catalyst in first riser reactor is led to fluid bed reactor. Preferred Component: The light material comprises gasoline fraction rich in hydrocarbon and/or C4 hydrocarbon rich in hydrocarbon obtained by production separation system. The hydrocarbon content in gasoline fraction rich in hydrocarbon is 20-95%. The distillation range of gasoline rich in hydrocarbon is 40-85 degrees C. The content of C4 hydrocarbon in C4 hydrocarbon rich in hydrocarbon is higher than 50 wt.%.