Abstract: In view of problems that load dynamic characteristics excited dynamic change of voltage and would cause voltage collapse under extreme case, the paper introduced slip ratio into load equivalent impedance model to analyze load impedance module and load impedance angle, which obtained catastrophe point of load impedance module and load impedance angle. It analyzed load dynamic characteristics by use of the model and discussed changes of voltage and power of node when load changed, which obtained turning points of node voltage and node power. It analyzed influence of different load proportion on static voltage stability of power system by an example through combining with voltage stability limit curve of transmission network which was deduced by three element voltage stability analysis method，so as to reach a conclusion that increasing proportion of constant impedance load would be helpful to enhance static voltage stability of power system.