A potting box for assembling a transformer comprises an inner wall and an outer wall. The inner wall is sleeved in the outer wall. A bottom plate connected to a bottom portion of the inner wall and a bottom portion of the outer wall to form a potting space for accommodating a first winding and a second winding. An inner side of the outer wall comprises a first support portion for supporting the first winding and an outer side of the inner wall comprises a second support portion for supporting the second winding. An iron core of the transformer penetrates through an inner side of the inner wall.