The invention provides a detection device for measuring thickness of a spacer. The detection device comprises a control part, a feeding part and a detection part, wherein the feeding part comprises afeeding pipeline; one end of the feeding pipeline communicates to the detection part while a feed inlet and a feeding assembly are arranged at the other end of the feeding pipeline, the feed inlet communicates to the feeding pipeline, the feeding assembly comprises an air cylinder, and gas sprayed by the air cylinder pushes a to-be-measured spacer to enter the detection part; a detection cavity isformed in the detection part, an electromagnet, a first photogate and a second photogate are arranged in the detection cavity a first mobile door is arranged in the lower portion of the detection cavity, a second mobile door is arranged on the side portion of the detection cavity, a movable push rod is arranged in the side wall of the other side of the detection part, a rejected product discharging pipeline and a qualified product discharging pipeline are also arranged on the detection part, the rejected product discharging pipeline and the detection cavity are separated through the second mobile door, and the qualified product discharging pipeline and the detection cavity are separated through the first mobile door.