Based on the chaos synchronization, a security-enhanced bidirectional long-distance chaos secure communication system is proposed. The results show that, under suitable parameters of dual-path injection conditions, low time-delay signature (TDS) and broadband chaotic signals can be generated from driving laser (DL). The chaos signals from DL are injected into two response lasers (RLs). By optimization of injection strength and detuning frequency, the optimized chaos signals with lower TDS and wider bandwidth can be generated and high-quality chaos synchronization between two RLs can be obtained. Meanwhile, the maximal synchronization coefficient between DL and RLs is lower than 0.1. Based on the high-quality chaos synchronization between two RLs, a security-enhanced bidirectional long-distance chaos communication can be achieved. Q factor of 20 Gbit/s decoded messages is more than 6 after a propagation over 120 km under dispersion shifted fiber used as channel, and Q factor of 1 Gbit/s decoded messages is more than 8 after a propagation over 140 km under normal single-mode fiber used as channel.