A potential method to produce the high-intensity keV high-order harmonic generation spectrum and the attosecond pulse has been proposed by using the inhomogeneous combined field. The results showed that with the proper superposition of two-color multi-cycle mid-infrared field and a few-cycle near-infrared field, the harmonic cutoff can be extended and a harmonic plateau contributed by the single quantum path can be obtained. Thereafter, by properly adding an ultraviolet pulse, the signal of the harmonic plateau can be enhanced by 500 dB due to the resonance ionization. Finally, by superposing some selected harmonics, some attosecond pulses shorter than 35 as can be obtained.
