The invention discloses a single-phase three-winding autotransformer model taking nonlinear influences of excitation impedance into consideration, which belongs to the technical field of transformers. The single-phase three-winding auto-transformer model comprises a basic electric circuit and magnetic circuit equation of a single-phase three-winding step-down autotransformer, an equivalent circuit of a single-phase three-winding autotransformer, an equivalent circuit of a single-phase three-winding step-up autotransformer, an expression of an excitation impedance zm and an expression of the single-phase three-winding autotransformer model taking account of the nonlinear influences of the excitation impedance. The autotransformer model not only takes account of the magnetic coupling between a high-voltage winding and a medium-voltage winding but also takes account of the electrical relationship, and the result of a harmonic characteristic simulation performed by the single-phase three-winding autotransformer model is more actual than that of the harmonic characteristic simulation performed by a common three-winding transformer instead of the three-winding autotransformer. The excitation impedance not only comprises generally non-ignorable nonlinear inductance reflecting iron core saturation characteristics, but also takes account of the nonlinear resistance reflecting iron losses, and the harmonic characteristic of a transformer can be analyzed more accurately by using the excitation impedance.