In order to solve the problem of flicker produced by EAF operation, it is a prerequisite to analyze the characteristics of voltage time series of EAF power supply grid and to conduct voltage prediction. The phase space of voltage time series is firstly reconstructed, the optimal delayed time and embedding dimension are determined using mutual information method and Cao"s method, and the maximum Lyapunov exponent is calculated, it is proved that the fluctuation voltage of the power supply grid has chaotic characteristics. Using the largest Lyapunov exponent method and weighted first-order local method to predicte the voltage in ultra short term. The results show that the chaotic prediction can reflect the EAF power supply grid voltage fluctuating trend, the ultra short term forecast precision is high, the latter one is better. Therefore, the weighted first-order local method is more suitable for predicting the fluctuant voltage of EAF power supply grid.