The compensated pulsed alternator (CPA) has high energy density and high power density, and can supply repetitive pulse, which can be used as a power supply for a variety of fields including laser and electromagnetic launchers. There are two stages for the operation of the CPA: self-excitation and discharging. It needs to generate an adequate current in the exciting windings as to supply a very large output pulse current when discharging. But it has a condition to realize a successful excitation. A successful excitation is very important for a successfully-designed CPA. This paper will analyze the excitation of the CPA and discuss the condition for successful excitations.