This paper discussed several key problems in the automatic annotation of linear elements,proposed to calculate the positioning line of a linear element using reference annotation line and to achieve dynamic segmentation of reference annotation line using reverse Douglas algorithm, using the segmentation result to choose smooth parts of linear elements as candidate annotation positions. On this basis,get the candidate position and score for every letter, then resolve the conflicts between annotations using taboo algorithm. The problem of vague and invisible representation of linear element annotations was solved and the integrity and aesthetics of automatic annotation output were achieved.