The dissociative ionization of ethanol C2H5OH in an intense laser field is investigated with a chirped laser pulse. From the sensitive dependence of the relative yields of the fragment ions on the absolute values of the linear chirp rate, it is shown that the light-dressed potential-energy surface (LDPES) at the singly charged stage governs the nuclear dynamics, and that the nuclear wave packet flow into the breaking of either of the C-C and C-O chemical bonds could be characterized by the holding time t(hold) during which the LDPESs are maintained. It is also understood in term of the holding time that the enhanced ionization into the doubly charged stage followed by the Coulomb explosion at C-C or C-O proceeds when the nuclear wave packet at the singly charged stage reaches the critical distance for the further ionization. (C) 2003 American Institute of Physics.