The utility model discloses an oil formula transformer has solved under the situation that takes place the oil leak, and especially under the less condition of the flow velocity of flow that leaks, the oil of leakage is difficult to discover soon, has just so leaded to the time of processing elongated. Its technical scheme main points encircle in the below of fin at the oil tank lateral wall to install the lateral part shell, shell bottom the lateral part shell is provided with bottom the oil tank, the lateral part shell has an opening up the change who meets transformer oil and discolour is placed to the inside cavity of lateral part shell and bottom shell. Having reached grease that the lateral part revealed and just having entered into that the cavity is inside to contact and take place the change of colour with becoming, the bottom shell that the oil tank bottom set up then can play to the oil of revealing of bottom and the contact that becomes the body card to the change of realization through the colour comes the warning and senses the oil formula transformer of oil leak situation rapidly.