The effect of DC magnetic field on the thermoelectric power of Al alloys at different temperatures was investigated in this work. The results showed that if the magnetic field intensity difference between the two ends of the sample was large, it would lead to a decrease in thermoelectric power of liquid Al-2.89%Fe Al alloys. When the magnetic field was removed, it took a period of time for the thermoelectric power to increase gradually to the initial value. This phenomenon had been observed in other Al alloys melt at different temperature. The higher the square difference of magnetic induction was, the more significant thermoelectric power changed. The approximate homogeneous magnetic field had no effect on the thermoelectric power. According to the theory of weak localization, the magnetic field can change the distribution of extended states electrons which contributes to the change of thermoelectric power.