In order to extract the line-features of extended object more quickly and more accurately, a line-edge extraction method is proposed based ergodic block. With proposed algorithm,a whole image is traversed by blocks,then the blocks with double peaks is obtained according to the property of gray-histogram.After processing those blocks by gray threshold and chain-edge extraction, the blocks without line characters are eliminated, the others with line characters are sorted by slope and intercept.Finally,the lines are got by computing the mean of similar slopes and intercepts. Experiment results show that proposed algorithm can extract line in subpixel precision and the precision of angle is higher than 0.01 rad. The complexity and computation of proposed algorithm is more better than that of Hough transform,which provides a way for hardware-implementation.