Multi-spectrum grid harmonic voltages are usually transmitted to the low-volatge bus connected to the delta winding through the three-winding transformer, and their prolonged action on the high-voltage shunt capacitor will affect its life and performance, but at present, there are few studies on the harmonic voltage transmission characteristics of the three-winding transformer containing delta windings. Therefore, this paper firstly establishes a single-phase harmonic equivalent model of a three-phase three-winding transformer containing delta winding and transformer parasitic capacitance based on the port equivalence principle, and derives the harmonic voltage transfer function between the high and low voltage side of a three-winding transformer based on the proposed equivalent model. The correctness of the harmonic voltage transfer characteristics is verified by comparing the data of the simulation model with the theoretical results.