The invention relates to a load transfer capability-considering offshore wind plant primary transformer capacity optimizing method. The method comprises the following steps of according to the total installed capacity of an offshore wind plant, giving gathered transformer substation primary transformer capacity selection schemes, selecting three values from small to large according to margin, and calculating the primary transformer investment cost of each scheme; calculating economic loss of each selected scheme, caused by primary transformer loss in the whole economic life cycle of the transformer, and taking the sum of the economic loss caused by primary transformer loss and transformer investment cost as the total cost of the scheme; on the basis of the output force characteristic of an offshore wind resource, calculating electric energy loss of each scheme, caused by the failure of one primary transformer in the whole economic life cycle of the transformer, and converting each electric energy loss into a benefit loss value according to feed-in tariff; taking the sum of the total cost and benefit loss value of each scheme as the evaluation standard of the benefit of each scheme, and performing cost benefit analysis on each type-selecting scheme of the transformer to obtain a transformer type-selecting scheme.