The invention discloses an on-site mixed emulsion explosive variable density segmented charging method and device. The device comprises a matrix conveying unit, a sensitizer conveying unit, an accelerant conveying unit, a water ring forming device, an explosive conveying tube reel and a controller for controlling the sensitizer conveying unit, the explosive inlet end of the water ring forming device is connected with the matrix conveying unit, the sensitizer conveying unit and the accelerant conveying unit through pipelines, and the explosive outlet end of the water ring forming device is connected with the explosive conveying tube reel. According to the device, the explosive density is adjusted in real time when an explosive is continuously charged in the same blast hole through variable-density segmented charging, and the technical defect that in the case that a single blast hole is filled with different density explosives, shutdown is required to adjust explosive production processparameters is solved.