The optical absorption spectra associated with transitions from the first valence subband to donor impurities are calculated in a three-dimensional corner under an applied electric field. It is found that there are two peaks for the absorption spectra in the corner, and the width of the absorption spectra increases with the increase in the electric field strength. The comparison between the optical absorption spectra in the corner and in a cubic quantum box shows that there is one absorption peak in the cubic quantum box, and the width of the absorption spectra in the equivalent quantum box is larger than that in the corner.