With the pervasiveness of Vehicle Information Svstem (VIS) and the advance of Vehicular Ad-hoc Network ( VANET).Intelli- gent TransportationSystem (ITS).which can improve road traffic and reduce the number of traffic accidents.has attracted considerable interest recentlv However.the flourish of ITS still faces many challenges including the privacy of individual data and locations In this paper.we propose a secure and privacy-preserving traffic flow analysis scheme.called PTFA.for ITS vith PTFA.user privacy can be guaranteed when the manager acquires the fine-grained traffic information In specific.we first map the information of roads to a superincreasing sequence;then construct an improved multi-dimensional aggregation scheme based on the homomorphic Paillier cryptosystem For data communications from user to traffic regional-center (TRC).data aggregation is performed directly on ciphertext at road side units ( RSUs) without decryption.and the aggregation result of the original data can be obtained at the TRC Detailed securitv analvsis shows that the proposed PTFA scheme can efficientlv achieve user privacy-preserving in ITS In addition.performance evaluations via extensive simulations demonstrate the PTFAs effectiveness in terms of providing fine-grained traffic information processing and minimizing communication cost.