Abstract: Resistance, reactance, and susceptance are estimated as independent variables in the conventional methods of parameter estimation. However, because they have a great difference in value, their estimation errors are inconsistent, especially the errors of small impedance are usually very large. Based on the length and the line parameters per unit length, a new line parameter estimation model is proposed. In this new model, state variables are multi-period voltage amplitude and phase angle at two ends of the line, and parameter variables are the parameters per unit length and the length. Because of introducing the length as the public variables of resistance, reactance and susceptance, the influence of line parameters on power flow is highlighted, so the consistency of line parameter estimation error can be guaranteed, and large estimation error of small impedance which appears in conventional models can be voided in the new model. Besides, the chaos quantum immune algorithm is presented to solve the parameter estimation model. It has the advantages of global optimality and stability. The validity of the proposed model and algorithm is verified by the simulation test.