A manufacturing method of heat conductive device for an LED has steps of forming a heat sink and an engagement recess in the heat sink by cold forge, punching a heat-conducting disc to form an LED carrier having a mounting portion and a heat-conducting wall formed around the mounting portion, soldering multiple LEDs on the LED carrier, and heating the heat sink to thermally expand the heat sink and assembling the LED carrier and the heat sink so that the heat-conducting wall is assembled with the engagement recess and further chilling the heat sink to thermally retract and tightly hold the LED carrier. The manufacturing method increases contact area and reduces air gaps between the LED carrier and the heat sink to effectively enhance the heat-conducting efficiency of the LED carrier so that the LEDs are operated at a suitable operating temperature to secure a prolonged life duration.