The classical minimal model with single compartment was modified by the assumption that the insulin decay rate is not always a first-order process, and a mathematical function for describing the insulin infusion rate is introduced. The modified model was used to study four sets of published data including healthy humans and Type 2 diabetes with different types of insulin infusion rates. The single-step fitting process took the glucose-insulin system as a dynamic integrated physiological system and generated the real optimized model parameters from the experimental data using the modified model. It also avoided the errors from the interpolation or extrapolation for taking measured insulin points as inputs, which were mostly employed in publications when using the single or multi-compartments minimal model. The averaged R(2) value between measured and calculated plasma concentrations for these four cases is 0.977, which indicates excellent agreement.