The invention discloses a start-up method of a fluidized bed-fixed bed combined process. The method comprises steps as follows: a catalyst is charged into a fluidized bed reactor and fixed bed reactors from the tops; a connecting pipeline between the fluidized bed reactor and the fixed bed reactors is pressurized for boosting; pressure penetrates through the fluidized bed reactor forwards and penetrates through the fixed bed reactors backwards respectively; after pressure is increased to meet the reaction demand, start-up oil enters the fluidized bed reactor and the fixed bed reactors from thepipeline between the fluidized bed reactor and the fixed bed reactors respectively for catalyst wetting; after catalyst wetting, start-up of the reactors is finished, and a device operates normally.According to the start-up method of the fluidized bed-fixed bed combined process, pressure drop of the device can be effectively reduced, the range of processed raw oil is expanded, and stable and long-periodic operation of the device is realized.