Continuum wavepacket interference is investigated by numerically solving the time-dependent Schröodinger equation for the interaction of hydrogen atoms with laser fields. The obtained wavepacket evolution indicates that, in the over-the-barrier ionization regime (10¹⁶ W/cm²), the continuum–continuum (CC) interference of ionizing electrons becomes the main process in highorder harmonics generation (HHG), compared with continuum-bound (CB) transition, as reported by Kohler et al. [Phys. Rev. Lett. 105(20), 203902 (2010)].We propose a two-color laser field scheme for controlling the quantum trajectories of ionizing electrons and for extending the CC harmonic energy. As a result, a high energy platform occurs in the HHG spectrum, which entirely originates from the CC harmonics, with a cutoff adjustable by the relative phase of the two-color fields. This provides further understanding of the dynamic feature of atoms and molecules in super intense laser fields and provides an opportunity to image the atomic or molecular potential.