In this study, we propose a high-speed secure key distribution scheme based on symmetric-phase-shift-keying chaotic synchronization. Using the delayed self-interference of an unbalanced M-Z interferometer, the correlation between the drive and response signals is reduced to 0.25. The eavesdropper cannot directly obtain part of the relevant key from the chaotic drive signal to improve the key distribution security. An open-loop chaotic synchronization structure is constructed by a commonly driven semiconductor laser without external cavity feedback, which avoid multiple oscillations of chaotic signals in the feedback external cavity in the closed-loop structure, shorten the recovery time of chaotic synchronization to 1.8 ns, and improve the key distribution rate. Finally, when the BER is 3.8×10^-3, a high-speed secure key distribution at a rate of 1.28 Gbit/s is realized.