The invention provides a transformer and a transformer bobbin thereof. The transformer bobbin includes a winding part, a first wire outlet part and a second wire outlet part; the second wire outlet part is provided with an inclined guiding surface facing the winding part, a first partition plate arranged on the inclined guiding surface and a wire avoiding groove arranged on one side of the inclined guiding surface; the inclined guiding surface is divided into a first wire outlet area and a second wire outlet area, the wire avoiding groove is only arranged in the first wire outlet area, and the first partition plate is formed with a wire supporting notch. Therefore, it is not necessary to add an insulation sleeve to windings at the same wire outlet part to achieve winding isolation, whereby windings on the transformer is automatically wound by a machine.