The invention relates to an online processing device and processing method for tank bottom sludge discharge of an oil field settling tank and belongs to the technical field of energy conservation and environmental friendliness. The online processing device is characterized by comprising a separator and a conveying unit, wherein a feeding opening of the conveying unit is communicated with a drain outlet (2) of the settling tank (1), a discharging opening of the conveying unit is communicated with a feeding opening of the separator, a mixed liquid outlet of the separator is communicated with a feeding opening of the settling tank (1), a sludge outlet is further formed in the separator, the conveying unit can convey the sludge at the bottom of the settling tank (1) into the separator, the sludge is washed and separated in the separator, separated oil-water mixed liquid is sent into the settling tank (1) again through the mixed liquid outlet, and separated sludge-water mixture is drained out through the sludge outlet. The online processing device for tank bottom sludge discharge of the oil field settling tank avoids a lot of oil and water loss and reduces oil sludge generation. The online processing method for tank bottom sludge discharge of the oil field settling tank has a simple processing technology and is convenient to operate, and the crude oil recovery rate can be 90%to 98% or more.