Small-world model based on equivalent admittance for power system is presented. Instead of shortest path used in the existed models, it is reasoned that the Theveninpsilas equivalent impedance can be used as measurement of the distance between different buses in power grid because the power flow is dividable which is quite different from the message flow in information network. Thus, global and local equivalent admittance are used to identify the small-world feature of power grid with more comprehensible physical view and polynomial time complexity. Numeric examples show that the presented model has the same effect as but more reasonable than the existed ones in power system, while it also works well in some situations in which the existed models are improper.