Abstract: It was difficalt to find a suitable system to determine the activity of immobilized glucose oxidase which was produced from entrapping enzyme by means of colorimetry from initail velocity assay. A two-step "Simulate system" and a convenient calibration formula A=A₀(1-e^-β[E]) were given in this paper. Where a was absorbed optical density,[E] was the concentration of the immobilized glucose oxidase, A₀ and β were constants under a given experimental condition. The more correct activity of immobilized glucose oxidase might be obtained by using the formula mentioned above.