A novel timing synchronization algorithm is proposed based on constant amplitude zero auto-correlation (CAZAC) sequence. In the proposed algorithm, the training sequence consists of four CAZAC sequences, which are divided into six timing windows. The correlation operation is carried out by use of the characteristics of conjugate symmetry and even symmetry of the sequences, and the timing metric function is obtained by multiplying these six timing windows. The simulation results show that the proposed algorithm can be used to obtain the timing metric function curve with the unique pulse peak and eliminate the disturbance of timing plateaus and side lobes. Meanwhile, the proposed algorithm has good timing stability within a large range of optical signal-to-noise ratio and chromatic dispersion.