The invention discloses a low-voltage distribution line distribution transformer three-phase unbalance protection method and device. The method comprises following steps: monitoring a low-voltage distribution line, acquiring three-phase current of the low-voltage distribution line in real time, and obtaining actual power supply load; calculating distribution transformer load rate [beta] and neutral point current I0 on the basis of the actual power supply load and the three-phase current of the low-voltage distribution line; when the distribution transformer load rate [beta] and the neutral point current I0 satisfying a first judging condition, calculating three-phase unbalancedness of the low-voltage distribution line distribution transformer; selecting corresponding risk pre-warning levels for processing the low-voltage distribution line three-phase load on the basis of the three-phase unbalancedness. The device comprises a monitoring acquiring module, a first calculation module, a second calculation module, and an execution module. By means of the method and device, the unbalancedness of three-phase current can be greatly reduced.