The transverse Stark shift of the electronic energy levels in GaAs semiconducting quantum box is investigated by the use of variational solutions to the effective-mass approximation. It is found an interesting phenomenon that the largest Stark shift is obtained for the electric field directed along the diagonal in cross section of a quantum box, while for a rectangular one, the shift reaches peak value for the low field directed along a side of cross section and for the high field along the diagonal. Likewise, the conclusion is shown that the transverse Stark shift in a quantum box depends highly on the ratio of cross sectional sides while is irrelevant to its height. The large Stark shift of the electron and hole trapped in a quantum box leads to an obvious reduction of the interband recombination and wide irradiance spectrum.