Installing compensation equipments is a good manner to improve line transmission capacity and maintain power system stability in the extra high voltage(EHV) long distance transmission line.It is of benefit to analysis and control by describing the effect of compensation equipment correctly.At present,for predigesting analysis or increasing real-time calculating speed,concentrated parameter circuit model is widely used to analyze 500 kV EHV long distance transmission line which may cause bigger error.So it is necessary to get a more reasonable model.On the basic of voltage and current distributed equations of even distributed long distance line,this paper deduces phasor diagram and power-angle character equations of uncompensated long line.Then the authors analyze the effect of compensators and define two characteristic parameters,namely,equivalent impedance x_(eq) and voltage coefficient K_V.Any compensating states of EHV long distance transmission line,example installing the compensators in the line or not or which type of compensators,is described by the general phasor diagram and power-angle characteristic equations.Furthermore,increment calculation(equations) of two characteristic parameters is presented by the compensator parameters which may make the concepts clear and predigests analysis easily.