Abstract: Differential current protection has been widely used for the line as main protection. Conventional differential current protection has relatively lower sensitivity because of charging current and heavy load; and may mal-trip for external faults with CT saturation, and the additional methods to avoid mal-operation from CT saturation may slow down the operation speed and sensitivity. Adaptive line differential protection enhanced by phase angle was proposed, which achieves good balance among high sensitivity, fast operation speed and high security. Proposed protection principle is immune to charging current and CT saturation, and has fast operation speed with small value of the operate time dispersion. PSCAD/Matlab simulation verifies the validity of proposed principle.