Abstract: A lamp socket mounting device includes a butterfly clamping plate mounted around a lamp socket to hold it in the socket mounting hole of a socket holder, wherein the butterfly clamping plate consists of a loop-like base frame portion mounted around the lamp socket, two curved, symmetrical upper stop frame portions bilaterally extended downwards from the loop-like base frame portion, two half-round bottom stop frame portions stopped against the socket holder at the bottom, and two neck portions respectively connected between the upper stop frame portions and the bottom stop frame portions and stopped against the periphery of the socket mounting hole, the upper stop frame portions having a respective bottom end terminated to a respective clamping edge stopped against the socket holder at the top.