By solving numerically the time-dependent Schrödinger equation with the split-operator method, we investigate the characteristic of the high-order harmonic of one-dimensional helium atom exposed to two laser pulses with the same color and half cycle pulses. It is shown that the harmonic spectrum is extended to Ip+9.6Up in the case of the combined fields, and an isolated 63 as pulse can be obtained by superposing the high-order harmonic spectra generated around the cut-off position. An analysis shows that the plateau of the high-order harmonic spectrum is extended greatly and the contribution of the long electron trajectory is suppressed by adding the half cycle pulses.