Wavelength division multiplexing (WDM) used in an ultrashort pulsed digital micro-holographic system to record and represent ultrafast processing of femtosecond scale is reported.A BBO crystal is used to generate the harmonic wave of the incident laser wave, and both the basic and doubled frequency waves are separated, then time-delayed respectively and introduced to a Michelson's interferometer to record two sub-holograms with different spatial frequencies on a single frame of a CCD by means of WDM. In the experiment, an ultrafast dynamic process of air ionization induced by a single femtosecond laser pulse is holographically recorded, and both intensity and phase images of the digitally reconstructed images are obtained through Fourier transformation and digital filtering, which show clearly the dynamic process of the plasma forming and propagating, with a time resolution of femtosecond scale. The related parameters are, exposure time 50 fs, exposure interval of 400 fs, as well as exposure frequency of 2.5×1012 f/s.