The present invention discloses a transformer oil leakage online blocking assembly, which comprises an isolating layer and a sealing cover, wherein the isolating layer covers a transformer oil leakage part, the sealing cover covers the isolating layer, a sealed air pressure cavity is formed between the sealing cover and the isolating layer, and a ventilation valve is arranged on the sealing cover. By adopting a method of covering and adhering the isolating layer on a leakage part of a transformer and applying a stress thereon, the pressure inside and outside the transformer can be balanced, thereby the purpose that the transformer oil does not leak in the blocking process is achieved, the problem that the transformer insulating oil leaks during the curing process of an adhesive when the adhesive is adopted for adhering and leaking stoppage is solved, the effective acting time of blocking is prolonged, the operation method is simple, the material is easily obtained, and the blocking is convenient to implement without cutting off power or discharging oil.