The application discloses subway engineering maintains car and auxiliary power supply system thereof, this auxiliary power supply system include that two sets of identical and subway engineering autonomous working separately maintain car auxiliary electrical power source, wherein: each cover subway engineering maintains that car auxiliary electrical power source includes: the auxiliary current transformer with pull the storage battery charging machine, the two sets of subway engineering maintain that the input/output side of the auxiliary current transformer among the car auxiliary electrical power source is all parallelly connected, two sets of subway engineering maintain that the input/output side of the storage battery charging machine that pulls among the car auxiliary electrical power source is all parallelly connected, have improved subway engineering and have maintained car auxiliary electrical power source's reliability, and then reduced the fault rate that subway engineering maintained the car.