The invention discloses a co-processing system and a co-processing method for humus and plastic in aged rubbish in a cement kiln. The system comprises an aged rubbish screening device, a rubbish incinerator and a humus pre-drying and thermal desorbing device. The method comprises the step of screening the aged rubbish and the step of incinerating rubbish, the step of screening the aged rubbish means separating the plastic product and humus from the aged rubbish, and the step of incinerating rubbish means feeding the separated plastic product into the incinerator for incinerating, pre-drying the separated humus and performing thermal desorbing treatment on the pre-dried humus. According to the invention, the collecting efficiency of the plastic is increased through the throwing sorter step; on the basis of the idea of 'dealing with waste by waste' and heat energy recycling, the heat energy released by the plastic combustion is used as the heat source of the humus thermal desorption; the exhaust gas after the humus thermal desorption is treated through an exhaust gas treatment system of the cement kiln, so that the treatment cost of the exhaust gas of the humus thermal desorption is saved.