The invention discloses a floor mopping robot obstacle avoidance method comprising the following steps: comparing supersonic wave actual measurement values with measured room length or width values, and determining whether an obstacle exists in certain unidirectional cleaning route or not; if yes, allowing the robot to stop moving, reversing a motor, and continuously moving; employing a left avoidance rule if a left turn is carried out in moving; employing a right avoidance rule if a right turn is carried out in moving; continuously moving forward according to moving rules after the obstacle is avoided; if not obstacle exists, allowing the robot to continuously move forwards according to moving rules, and determining whether an enough space is provided for the robot dust collector to take turns or not before turning; turning the dust collector if enough space is provided, and finishing the unidirectional cleaning; if the dust collector cannot take turns, an obstacle is determined in the start point of the next unidirectional cleaning, allowing the robot to move backward, avoid the obstacle and take turns again, and moves forward until passing the obstacle sideline, thus finishing the unidirectional cleaning.