The model of phase retardation shift between the two polarization modes of polarization maintaining fiber (PMF) caused by partially discharging is established. The Panda polarization maintaining fiber (P-PMF) and polarization maintaining photonic crystal fiber (PM-PCF) are investigated respectively in a Sagnac interferometer. The results show that the phase retardations of stress-induced P-PMF and shape-induced PM-PCF will decrease and increase respectively after being partially discharged, and the shift of phase retardation can be effectively changed by adjusting discharging current and duration time, which provides a practical technique for redressing the phase retardation of polarization modes in PMF. An on-line waveplate fabrication setup is established and the fabrication of PM-PCF quarter waveplates is experimentally investigated. A phase retardation precision of 0.15° is achieved. The repeated experimental results demonstrate that the precision of phase retardation can reach about 0.24°. The proposed technique is simple and cost-effective, which can improve the phase retardation precision and the fabrication efficiency of fiber optic waveplates.