Coherent control theory was applied to a coupled system by a time-dependent approach. Then it is used to stimulate the control of the relative product yield of the photodissociation of CH3I and IBr, respectively. The calculation shows that it is possible to vary I/(I + I*) over the range of 2-74% in dissociation of CH3I and Br*/(Br + Br*) over 9-94% in the dissociation of IBr.