The waste plastic gasification in a fluidized bed for a continuous carbon nanotube (CNT) and hydrogen coproduction is a potential method for sustainable management. Ni/Al2O3 catalysts have been synthesized by the impregnation method to upgrade hydrogen production and CNT synthesis. However, few studies investigated the effect of operating parameters for upcycling waste plastics into CNTs and hydrogen in the fluidized-bed system. The reaction temperature and the equivalence ratio (ER) were evaluated for CNT and hydrogen coproduction. Increasing the reaction temperature and lowering the ER enhanced the methane dry reforming, hydrocarbon dry reforming, and hydrocarbon direct decomposition for hydrogen and CNT coproduction. While increasing the reaction temperature from 500 to 700 °C can obtain higher CNT yield and H2 production rate, the system heated to 700 °C and maintained at this temperature should provide more energy. Moreover, the gas composition at 600 °C with 0.1 ER contained more CH4 and C2–C5 hydrocarbons compared with that with a higher ER, which could be used as the carbon source of CNTs. The reaction temperature of the fluidized bed in the waste plastic gasification system controlled at 600 °C with 0.1 ER and the gasified products upgraded through a catalytic fixed-bed reactor at 680 °C exhibited an optimal catalytic performance of less-defective CNTs in 22.0% yield and H2 production rate (385.1 mmol/h-g catalyst).