The existing form frame line detection algorithms are either time consuming or with low robustness. Furthermore, all these approaches do not use the constraint information between form frame lines. In this paper, a novel bottom-up form frame line detection algorithm is proposed based on the directional single-connected chain (DSCC). Defined as an array of black pixel run-lengths, DSCC works very well as an image structure element or a vector in this vectorization algorithm. By merging multiple DSCCs under some constraints,people are able to extract the form frame lines automatically yut fast.With the help of the con straints between form frame lines,the robustness of the approach is increased drastically by getting rid of pseudo lines and completing broken lines.Byfiltering DSCCs created by noise and speeding up the merging of DSCCs,the speed of this algorithm is comparable with the well-known projection method.Experimental results show that this algorithm is fast,resistant to moderate serious line break and skew of any angle.