A method for determining a state of charge adapted for a battery is provided, the method including: obtaining a plurality of discharge curves; determining that the battery is in a discharge mode; measuring a current C-rate and a current voltage of the battery in the discharge mode; selecting a first discharge curve and a second discharge curve from the plurality of discharge curves, wherein a first C-rate corresponding to the first discharge curve is greater than the current C-rate, and a second C-rate corresponding to the second discharge curve is less than the current C-rate; and calculating a state of charge of the battery according to the first discharge curve and the second discharge curve.