Privacy-preserving data mining is discovering accurate patterns and rules without precise access to the original data. This paper focuses on privacy-preserving research in the situation of distributed decision-tree mining, and presents a decision-tree mining algorithm based on homomorphic encryption technology, which can get accurate mining effect in the premise of no sharing of private information among mining participators. Theoretical analysis and experiment results show that this algorithm can provide good capability of privacy-preserving, accuracy and efficiency.