The invention provides a device for detecting explosive detonation velocity in a blast hole. The device for detecting the explosive detonation velocity comprises unit structures. Each unit structure is composed of transverses boards (1) and a vertical bar (2), wherein sliding grooves are formed in the transverse boards so that the distance between the unit structures can be adjusted. The diameter of the detection device is the same as the diameter of the blast hole, therefore, the detection device can not make lateral movement in the blast hole, and the distance of probes and the propagation distance of explosive waves are guaranteed to be the same. The distance between the unit structures can be adjusted so that the explosive detonation velocity in blast holes of different diameters can be detected. Further, the detection device is simple in manufacturing, cheap, convenient to use, and capable of truly reflecting the actual explosive performance of the explosives in the blast holes.