Dispersive waves of mid-infrared band generated when the ultrashort pulse is launched into hollow-core Kagome photonic crystal fiber filled with Krypton gas are numerically investigated with the unidirectional pulse propagation equation. Two types of input pulses are studied, including a Gaussian pump centered at 1.4 μm and a near-saw-tooth-shaped two-color pulse centered at 1.4 μm added with its second harmonic. Multiple dispersive waves are observed under the two situations which are in agreement with the phase-matching conditions. In order to optimize dispersive waves, the near-saw-tooth-shaped pulse is used as the pump pulse. The second ionization of Krypton gas filled in fiber is caused by pump pulse compression, so that the earlier-generated dispersive waves are converted to new ones at longer wavelengths. This observation is legitimately explained by the plasma corrected phase-matching condition. The mid-infrared ultrashort pulse generation and the dispersive wave theory are discussed.