Provided is a bulb holder locking apparatus, comprising a fixing mount, a bulb holder, a spring and a ratchet mechanism comprising a ratchet bar having a plurality of ratchets, a pawl and a movable cam having a curve contour; wherein the bulb holder is flexibly connected to the fixing mount; the spring is connected to the fixing mount, so as to force the bulb holder to move downwards; the ratchet bar is connected to the bulb holder; the pawl is connected to the fixing mount and elastically contacted with the ratchet bar; the movable cam is slidingly connected to the ratchet bar and elastically contacted with the pawl; and the curve contour comprises a plurality of crests engaged with the pawls.