  Cooper minimum structure of high-order harmonic spectra from atoms or
molecules has been extensively studied. In this paper, we demonstrate that the
crystal harmonic spectra from an ultrashort mid-infrared laser pulse also
exhibit the Cooper minimum characteristic. Based on the accurate band
dispersion and k-dependent transition dipole moment (TDM) from the
first-principle calculations, it can be found that the harmonic spectra from
MgO crystal along {\Gamma}-X direction present a dip structure in the plateau,
which is originated from the valley of TDM by examining the distribution of the
harmonic intensity at the k-space. The Cooper minimum feature in crystal HHG
will pave a new way to retrieve the band information of solid materials by
using HHG from the ultrashort mid-infrared laser pulse.
