After comparing the traditional LiNbO3 Mach-Zehnder electro-optic modulator bias control techniques, a novel bias control method based on fast Fourier transformation (FFT) algorithm and the harmonic response feedback of a low frequency dither tone is proposed. Using this technique, a precise optoelectronics bias control system is realized to lock the modulator at an arbitrary point within its transfer function. This bias control technique is found to be independent on the optical input power and the insertion loss of modulator. Moreover, the proportion integration differention (PID) control method is used to optimize parameters and achieve a locking accuracy better than 0.5°. In addition, this bias control system is also verified experimentally to set and lock the modulator at an arbitrary bias point. Those results are helpful to stabilize the LiNbO3 Mach-Zehnder modulator at the optimal operating point and achieve an ultra-high speed, long haul optical fiber communication system.