The invention discloses an embedded combined type ultrathin transformer applied to an LED (light-emitting diode), comprising a cover, an inner disc and an outline border, wherein the inner disc is arranged in the outline border, the cover is arranged on the outline border, a transformer coil is coiled on the inner disc, a wire rod outgoing line of the transformer coil is led out from an outgoing groove on the inner disc, a pin is arranged on the outline border, and the wire rod outgoing line is firmly welded on the pin. The embedded combined type ultrathin transformer applied to the LED has the advantages of simple structure and ingenious design, can realize that the transformer is thinner without influencing the strength of the pin because the pin of the transformer is arranged on the outer border and the coiling inner disk has no pin, , is very convenient and practical because the occupying area of the PCB (printed circuit board) is also smaller, has good economic prospect, and can produce good social benefits.