Based on the method of depth from defocus(DFD) proposed by Pentland,we propose an approach to estimating the depth of the object by local lines considering the continuity of surface points of the object and faintness of image edges in the defocus images.We only need one picture to estimate the depth by adopting the method,so it can overcome the problems of matching and covering between pictures,and it has little computation and high efficiency.At the same time,the arithmetic is not sensitive to the noise because differential operation is not needed in this algorithm.Furthermore,depth correction method is used to improve measure precision.Experimental results prove that this arithmetic has high stability and credibility,with the measure error of depth under 2%.