To address the difficulty of traditional transformer protection in effectively identifying early-stage faults such as minor inter-turn short circuits in transformer windings, this paper proposes an early fault protection scheme for transformer windings based on the phase change characteristics of the leakage magnetic field. First, an analytical model of the leakage magnetic field for a transformer with a non-ideal winding structure is established, and the variation of magnetic leakage distribution before and after winding failures is analyzed. Then, by combining the fault components such as magnetic leakage phase mutation, phase differences among multiple measuring points, and leakage amplitude ratio, a leakage phase differential protection criterion and a fault location logic are proposed, effectively avoiding the influence of temperature on the optical fiber measurement system. The leakage magnetic field analytical model is also used for setting the operating thresholds of the protection scheme. Finally, the feasibility and effectiveness of the proposed early fault identification and location scheme are verified by dynamic model experiments and finite element simulations.