In estimating the channels for OFDM, ESAE has better performance than PSAM. But ESAE has the "run-away" phenomenon if the channel estimation errors accumulate. In the proposed Assisted Pilot for Improvement and stability of Mobile communication system (APIM) method, pilots used in PSAM, additional pilots and some pre-estimated channels are applied to estimate the channel. The experimental results show that the proposed method, APIM, significantly outperforms conventional methods in terms of MSE and BER under Rayleigh fading environment and has stable characteristics even in the high-speed mobile communication system.