Abstract: In order to measure the phase of mid-infrared field and to obtain the attosecond pulse, the investigation on mid-infrared field phase measurement and attosecond pulse generation has been presented by using the relationship between phase and harmonic cutoff energy. With the introduction of a few-cycle pulse to mid-infrared field, the effect of phase of the combined field on harmonic cutoff energy became much more distinct in comparison with the single field. One new method of phase measurement was gotten. Further, harmonic extension spectra and attosecond pulse generation of the three-color mid-infrared field were numerically investigated. The results show that by properly adjusting the delay times and phases of three pulses, not only harmonic cutoff energy is extended, but also single quantum path is selected to contribute to the harmonic generation, resulting in supercontinuum with bandwidth of 272eV. Finally, by superposing the properly selected harmonics in supercontinuum region, a series of X-ray pulses with pulsewidth of 34as can be obtained. The investigation is helpful for phase measurement of mid-infrared field and attosecond pulse generation.