The invention discloses a determination method of capacity demand of main transformers in a power supply region based on transformer load levels. The method comprises steps of investigating operation states of each transformer station included in a power supply region, wherein the operation states of each transformer station are obtained according to the main transformer quantity, transformer station load and capacity of single main transformer; and obtaining judgment about whether transformer stations need to be expanded or whether the transformer stations need to be listed into a reserve warehouse of a planned project in the power supply region whose capacity-load ratio is within a value range by combining the growth rate function of annular load of transformer stations in the power supply region and giving out a quantitative determination method.