With the development of economy and increase of electro-capacity in our country, large capacity 1000MW power units will become the main force of power system. As a result, the auxiliary power system wiring will be complex due to the increasing of capacity and types of auxiliary machines, at the same time, the problems of large short circuit current and difficulty of motor starting are appearing. The ETAP software is used to model three projects of auxiliary power system for 1000MW units, they are project one (lOkV one voltage grade three sections wiring), project two (6kV one voltage grade four sections wiring), project three (6kV one voltage grade three sections wiring). The reliability, power flow and short circuit current of system are calculated and motor starting checkout is carried through. Meanwhile, the economic data and power consumption rate are given in this paper. The data of the three projects are integrated and analyzed to supply references for the future designing.