To solve the problem that the permutation graphic is too weak, a logistic-based watermark algorithm is proposed. On the basis of information about the copyright owner and legal user, initial value for logistic map is calculated and then chaotic sequences and watermark value are computed. After choosing the length of permutation graphic randomly, the copyright owner generates permutation graphic to embed into host program. According to similarity rate extracted from host program, the ownership of host program is identified even though the permutation graphic was attacked. The experimental results and theoretical analysis show that this scheme is more robust than traditional permutation graphic system and can resist common attacks.