The invention discloses a concrete slump testing device. The concrete slump testing device comprises a testing barrel, a trolley, a tamping mechanism, a measuring mechanism and a cleaning mechanism, wherein a flat plate with adjustable height and angle is arranged on a table board of the trolley, has three-dimensional adjusting capacity and can be leveled conveniently; a first portal frame and a second portal frame are arranged on linear slide rails on the table board, the tamping mechanism is arranged on the first portal frame, the measuring mechanism is arranged on the second portal frame, the cleaning mechanism is arranged on the flat plate and matched with a blanking port in the table board for use, and a concrete recycling tank is fixed below the blanking port. The concrete slump testing device is suitable for the in-situ concrete slump test, the levelness of a testing platform can be adjusted according to fields, the precision of a measurement result is guaranteed, tamping, demoulding strength and a process are more normative, and support is provided for accurate measurement of concrete slump.