There is a special area in KTP crystal, in which the SHG efficiency is obviously increased. In this paper, the KTP crystal is studied by means of Synchrotron Radiation (SR) White Beam Topography, and a planar defect is found in such an area. The lattice is deformed because of the accumulation of impurity in this area, which results in the increase of SHG efficiency. The maximum strain direction is determined to be R=〈010〉 according to the extinction condition of planar defect.