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We experimentally investigated the atomic ionization process in an XUV and IR laser fields, where the XUV pulse train was generated by high-order harmonic generation (HHG).Comparing with the electron spectrum ionized by XUV pulse train,the electron spectra generated by two-color field exhibited two characterizations: (1)the spectrum was smoothed in the presence of a weak IR field; (2) the spectrum was broadened with an intense IR field.Simulation results based on nonadiabatic quantum electrodynamic theory agreed well with experimental data.We demonstrated that the ionization process could be interpreted by a two-step ionization model in frequency domain, and the experimental observations originated from absorbing or emitting IR photons after the electron excitation of XUV photons.