The high-order harmonic generation (HHG) power spectra from a one-dimensional model atom irradiated is numerically calculated by linearly polarized 8 fs bichromatic laser pulses composed of a fundamental Ti:sapphire and its second harmonic lasers. It is found that,the distinct double plateau structure appears when the relative phase is zero,and an isolated 110 as pulse can be obtained from the continuous harmonics at the end of the second plateau. This validates Yu Oishi′s experimental research conclusion that continuous harmonic spectra can be obtained at specific relative phase between the fundamental and its second harmonic lasers. The numerical results have been explained by a “three-step” model. Finally,the wavelet time-frequency analysis adopted verifies that the “three-step” model could exactly predict the cut-off frequencies of the bichromatic pulse HHG spectra.