This paper investigates the nature of a flux switching permanent magnet (FSPM) machine based on the flux harmonic theory. First, analytical expressions for air-gap flux density distribution, back-electromagnetic force (EMF), and torque are developed to analyze the electromagnetic features of FSPM machines. It is found that the conventional winding theory, such as star of slots, can be directly employed to analyze FSPM machines without any modification. Combinations of stator and rotor teeth, winding connection, and conditions for symmetrical-phase back-EMF waveform are analyzed and obtained using star of slots. The armature winding pole pairs of FSPM machines are redefined. Based on this new concept and the proposed analytical expressions, slots per phase per pole and winding factor in FSPM machines are derived, a new type winding configuration with overlapping windings for FSPM machines is predicted and verified to be with similar to 90% larger back EMF than those of conventional FSPM machines with nonoverlapping windings. All these analysis results are validated by finite element analyzes.