Aiming at the problems that the existing dynamic equivalent modeling based on component mechanism may lead to the complex model structure and the difficult parameter identification, by introducing a feature modeling method with simple model structure and easy engineering implementation, this paper models the dynamic equivalence of the lower-level grid (or regional grid) online and realizes the hierarchical and zonal modelling of modern power grids. Firstly, the input and output variables of the characteristic model are determined by theoretical analysis and simulation comparison. Voltage is selected as the input variable, while the real part and imaginary part of current are selected as output variables. Then, to address the problem that the operating conditions of actual grid change at any time, the recursive least squares algorithm is used to identify the slowly-time-varying parameters of the characteristic model, when the component mechanism model undergoes slow time-varying. The results show that the fitting error of this kind of characteristic model is small, and the parameters have high stability.