The invention discloses a forward osmosis membrane bioreactor with magnetic nanoparticles serving as driving liquid and relates to a forward osmosis membrane bioreactor. The forward osmosis membrane bioreactor mainly solves the problems that existing forward osmosis membrane bioreactors uses inorganic salt as the driving liquid, and a salt solution osmoses into the bioreactor and has an inhibitory effect on microorganism, so that the sewage treatment effect is reduced. The bioreactor comprises a liquid storage pot, a water inlet pump, a first water inlet valve, an aerator pipe, a biological reaction tank, a mud valve, a forward osmosis membrane, a driving liquid tank, a second water inlet valve, a third water inlet valve, a first liquid storage tank, a second liquid storage tank, a first electromagnetic field, a second electromagnetic field, a first water drainage valve, a second water drainage valve, a first backflow valve, a second backflow valve and a pump, wherein the liquid storage tank is connected with the biological reaction tank through the water inlet pump and the first water inlet valve, the aerator pipe and the mud valve are arranged on the biological reaction tank, the forward osmosis membrane is connected between the biological reaction tank and the driving liquid, and the driving liquid is filled in the driving liquid tank. The forward osmosis membrane bioreactor is applied to the field of sewage treatment.