Abstract: A fundamental criterion for selecting a proper model in speci fied experiment requires the unbiased estimates of parameters in the model. In terms of author's former paper "Estimate of Parameters and its Uniqueness in a Model of Additional Experiment with Multifactors" a rigorous description is given in this work, in which the parameter estimates in the model are unbiased under the condition of the orthogonal imposed on all interactions among the factors, and the condition of normal distribution of the errors.