The defect of lack of penetration in Friction stir welding is the most common defect in thebottom of the weld. The properties of tension and fatigue are reduced, due to the characteristics of close, complex orientation and so on. The eddy current testing is used in this experiment, which has high sensitivity to the defect of surface and near surface. The Eddy Current Conductivity testing instrument is used to analyze the conductivity distribution on friction stir welding, which is affected by the direction of LOP. The results show that the conductivity distribution is affected by LOP's direction. Due to the strength of eddy current is decreasing exponentially from the surface of testing sample, and the distribution of eddy current is affected strongly by the opening of LOP, and the motion of electron transfer is blocked strongly by LOP, the location of the lowest conductivity to LOP of different direction is in the opening of LOP on each weld. With the decreasing of direction angle alpha(2), the location of the lowest conductivity to LOP of different direction is deviating from the weld center gradually.