Abstract: Aiming at the problem of edge broken easily produced in traditional chain code tracking, this paper presents an improved Freeman chain code for edge tracking and straight line extraction. this algorithm records the starting point of chain code and priority tracks points which are located in edge direction. For current point, it firstly tracks inside the eight neighborhoods with Freeman chain code, if there are no edge points in the eight neighborhoods, it will tracks outside the eight neighborhoods. Then it extracts straight line chain codes by edge chain code splitting. The experimental results show that this algorithm not only can effectively extract straight lines, but also can extract curve edges, and it keeps the continuous of edges to avoid lines connecting in after.