The electric load of Zhejiang Province is growing rapidly, and peak-valley difference is increasing by years. The duration of peak load only lasts for a short time.As energy storage technology is developing rapidly and the cost of it is falling, energy stor-age gradually becomes an important measure of reducing peak-valley difference. Aiming at the reality of Zhejiang power grid, the costbenefit analysis of electrochemical energy storage is modelled. This model of peakanalyses the econmic benefit, calculates the price difference- valley which can bring benefits and the dynamic paybackperiod under current electricity price policy. Finally, the prospect of energy storage technology is forecasted.