Abstract: For the OFDM(orthogonal frequency division multiplexing) systems with guard band, the permissible biggest guard bandwidth is computed on the bases of the conventional UPPTS (uniformly placed pilot tones sequence) design and the premise that the MSE(mean square error) of the LS(least square) channel estimation must be minimum. Thus, the choosing range is given for the initial position of pilot tones sequence to enable the sequence to avoid guard band efficiently by way of adjusting the initial position. Simulation results showed that the system can give higher precision of channel estimation and lower BER(bit error rate) when the initial pilot tone falls into the choosing range mentioned above. The effectiveness and advantages of the presented algorithm are thus verified further.