Abstract: It is difficult to protect software copyrights. In order to improve the robustness of software watermarking, a new software watermarking algorithm is proposed combining the advantages of Pareto Diagram, Planted Plane Cubic Tree (PPCT), Hash function and random number. Hash function and random number are used in preprocessing to hide the real copyrights information. The Pareto Diagram is created by modifying the left and right points of the leaf nodes of the PPCT. Both the PPCT and Pareto Diagram can be used to prove the copyright when it is in a copyright disputes. Even when the code pointers have been attacked, this algorithm will make use of the Pareto Diagram or the random number to reconstruct the PPCT of the watermark information which is embedded in programs. Even in the case of partial extraction，it also can provide evidence for the proof of copyright according to the similarity of reconstructing and extracting PPCT and in this way it further enhances the robustness of the software watermarking. The experimental results show that the proposed system can prove the privacy when some points in software watermark have been deleted, modified, or added and it significantly improves the performance against attack.