In wireless communication, the channel response may vary rapidly when the user's mobility is high. Since pilot signals are usually limited, channel estimation often involves interpolation. How to perform channel interpolation/estimation in high-mobility scenario is then a challenge problem. This is particularly true for an OFDM system operated in long-delay-profile channels. In this paper, we consider the channel estimation problem in IEEE802.16e systems. Using the special structure defined in the system, we propose an effective channel estimation algorithm. The main idea is to perform a two-dimensional interpolation with a cascade of two one-dimensional interpolations, one is linear and the other is nonlinear. Simulations show that this method has good performance while its computational complexity is low.