The invention relates to a transformer substation capacity optimization method based on multi-energy collaborative supply, and belongs to the field of energy internet and power distribution network planning. The method comprises the steps that an operation economy model is established according to energy utilization efficiency of a thermoelectric co-generation machine set in a tri-generation machine set and a cold and thermal conversion ratio COP value of a lithium bromide machine set based on the historical data of a transformer substation; capacity of phase change energy storage equipment is determined by the supply and demand relation balance of a typical day, and an operation cost function of the phase change energy storage equipment is determined according to energy storage efficiency; start and stop time arrangement of the tri-generation machine set with optimal economy is solved through a multi-target optimization method performing on the operation economy model and the operation cost function; multi-target optimization is performed on the annual electricity load characteristics by utilizing distributed photovoltaic component power generation; and the optimized capacity of the transformer substation is obtained under the principle of "N-1" and the standard capacity-load ratio requirement according to the optimized load side characteristics. The electricity utilization peak in the summer can be reduced and power supply pressure of an electrical network can be reduced.