Abstract: A relativistic differential VLBI(ΔVLBI) mathematical model for CE-1 in Earth-Moon transfer orbit is derived.Based on the model,ΔVLBI time delay observations are formed by differencing CE-1 time delay observations with a simulated radio source's time delay observations.Then unknown parameters including orbit of CE-1 and Earth Orientation Parameters(EOPs) are estimated under the least squares adjustment,in optimal parameter apriori accuracy,and the best arc length is determined according to the inner and externally coincident accuracy of each parameter.Finally,the accuracy of each parameter is given.