A polarity compensation device and a polarity compensation method are provided. The polarity compensation device includes a variance calculation circuit and a compensation calculation circuit. The variance calculation circuit calculates a difference value between current sub-pixel data and previous sub-pixel data in the same frame period, wherein the current sub-pixel data and the previous sub-pixel data belong to the same data line of a display panel. The compensation calculation circuit converts the difference value into a function value. The compensation calculation circuit decides to increase or decrease the current sub-pixel data by the function value according to a polarity corresponding to the same frame period, so as to generate compensated sub-pixel data.