This paper deals with an efficient method for channel estimation in Orthogonal frequency-division multiplexing (OFDM) systems. The channels are assumed to be Time-varying (TV) and approximated by a Secondorder polynomial (SOP) model. Increasing the polynomial order reduces the model error, but requires more polynomial estimation time. In order to circumvent the problem, we construct two SOP models by using a repeated-pattern preamble and pilots. As the channel information can be obtained from the second SOP model which polynomial estimation period is shorter than that of general SOP model, the proposed scheme is superior to the existing methods. Simulation results are presented to illustrate the superiority of our proposed approach.