As a new ultra-capacitor energy storage device, due to its low terminal voltage, typically requires the use of a plurality of ultra-capacitors connected in series. In addition to the effects of dispersion of the series between the ultra-capacitor banks, the voltage equalization is evolving. This paper describes various methods to equalize ultra-capacitors and then classifies them according to the nature of equalizing. The introduction of each method is presented one by one, as well as the comparison and summary.