The invention provides a dual-insulation transformer and a transformer insulation resistance testing method. Sleeves are arranged on the two sides of the upper end of transformer bearing plates. A first auxiliary damping device is arranged in the sleeve; a placing plate is fixed at the upper end of the sleeve; a protection box is arranged above the placing plate; two transverse plates are fixed tothe opposite side walls in the protection box. Two sliding grooves are formed in each of the two transverse plates; two sliding blocks are installed in each sliding groove, the two sliding blocks onthe same side form a set, a protection case is fixed to the upper ends of the two sliding blocks in the same set, the lower ends of the two protection cases move through movement of the sliding blockson the sliding grooves, connecting rods are fixed to the two protection cases, moving blocks are fixed to the connecting rods, and two moving rods move in the opposite directions; a bearing table with a cavity is fixed between the bearing plates, and a second auxiliary damping device is arranged in the cavity. The invention further provides the testing method of the insulation resistance of the transformer, the transformer is reasonable in structure, and the structure and the method are combined to achieve protection of the transformer.