The invention provides a method for repairing and strengthening a head of a cross head type eave rafter of an ancient building. The method comprises a step of cutting off a rotten rafter head, fittingone end of the rafter head and making an L-shaped section matched with an end part of the remaining rafter, a step of engraving a hooked convex tenon at an end part of the fitted rafter head, engraving a dovetail mortise at the middle part of a vertical surface of the section, engraving a dovetail mortise at an end face position of an original rafter, and engraving a hooked mortise at the section, a step of making a double-dovetail insertion tenons, a step of making a sole timber, engraving an arc groove at a surface of the sole timber connected to a purline, engraving a flat notch on the opposite side of the arc groove, engraving a rectangular mouth on the flat notch, making a rectangular insertion tenon and fixing the sole timber and the purline together by insertion connection, a stepof connecting the fitted rafter head and an original rafter together through the hooked tenon and inserting the double-dovetail insertion tenons into dovetail mortises, and a step of clamping the inserted rafter into a flat notch of the sole timber to strength and repair a rafter head part of a cross head arrangement of a wooden rafter in an ancient building roof structure layer on the basis of not changing raw materials and construction technology.