Current channel estimation methods usually assume that the channel coefficients within an Orthogonal Frequency Division Multiplexing(OFDM) symbol period are constant. However, in high-speed scenario, the channels within an OFDM symbol vary obviously. The Inter-Carrier Interference(ICI) will affect the performance of conventional channel estimation methods, which degrades the performance greatly. A method in which the variations of wireless channels are modeled in the form of power series is proposed. The number of channel coefficients is reduced greatly by converting the time-varying channels to the projections of finite parameter variables on the basis of power series. Theoretical analysis and simulation results show that the method can achieve a good performance by tracing and estimating the time-varying channel coefficients efficiently.