The invention discloses an air duct system, an air conditioner indoor unit and an air conditioner. The air duct system comprises a shell, a cross-flow fan and a radiant panel assembly, wherein the shell is provided with an accommodating space; an air outlet and at least one air inlet which communicate with the accommodating space are formed in the shell; the cross-flow fan is accommodated in the accommodating space, and is positioned between the air inlets and the air outlet; the radiant panel assembly is arranged on one side of the shell; the radiant panel assembly comprises a plurality of radiant panels which are arranged at intervals; one air duct is formed between the two adjacent radiant panels; and the air outlet right faces the air ducts and the radiant panels. The invention aims toreduce noise, reduce power consumption, increase the energy efficiency ratio and improve comfortability of the air conditioner indoor unit and the air conditioner which adopt the air duct system.