Due to the different distribution of energy distribution and power demand in China

the study of demandand scale of receiving-end grid is particularly important. To study reasonable UHV external power demand and scaleof receiving-end grid

this paper uses the convolution method based on probabilistic criteria of calculation to obtainthe reliability index

and calculates the external power demand of the regional power grid by using the reliabilitytheory

and then through the static security and stability of power grid

plan the capable of transportation scale.Finally

an example is analyzed to obtain the external demand and scale. The method is proved to be correct.