We propose an approach of long-term stabilization of optical fiber phase by controlling a piezo-based phase modulator and a Peltier component attached to the fiber via a phase-locked loop(PLL) circuit with dual proportional-integral- derivative(PID) adjustment. With this approach, we can suppress the fast disturbance and slow drifting of optical fiber to satisfy the requirements of optical phase long-term locking. In theory, a mathematical model of an optical fiber phase control system is established. The disturbance term induced by environment influence is considered into the PLL model. The monotonous and continuous changing environment disturbance will cause a steady-state error in this theory model. The experimental results accords well with the theory. The steady-state performance, adjusting time, and overshoot can be improved by using the dual PID control. As a result, the long-term, highly stable and low noise fiber phase locking is realized experimentally.