To provide a phosphorus-added high tensile strength galvannealed steel sheet free from local inferior adhesion of plating and a method for manufacturing it at a low cost with superior productivity without complicating an operating process and an operation controlling method.

In the galvannealed steel sheet constituted by forming a galvannealing layer on a steel sheet containing ≥0.02 wt.% phosphorus as a steel components, a metal easily forming a phosphorus compound is incorporated by (5 to 1000) mg/m2 into the plating layer and also the dispersion of thickness of Γ-phases is regulated to ≤±0.3 μm. At the time of allowing an oxide containing, as a cation, a metal easily forming a phosphorus compound to adhere to the surface of a steel sheet containing ≥0.02 wt.% phosphorus in the steel, carrying out heating in a reducing atmosphere, and then performing continuous hot dip galvanizing, the metal is allowed to diffuse into ferrite while performing the reduction of the oxide and is allowed to form a phosphide together with the metal.