This invention discloses double riser catalytic cracking device used to decrease sulfur content in catalytically cracked gasoline in petroleum processing field and solve the high sulfur content problem in existing technique. The device comprises heavy oil riser reactor (12) and gas riser reactor (4); set expanding- structural cylinder layer-shape reactor (2) below the raised air inlet (141); set pre-rise medium inlet (101) on vertical pipe below the layer-shape reactor; and use desulfurization catalytic cracking catalyst. It can decrease the sulfur content greatly and the olefin content, and increase octane number of gas.