With the continuous development of Arctic resources, the risk of collision between polar ships and level ice is increasing. Different icebreaking methods will have different effects on the hull structure under variable ice thickness. At present, the judgment of icebreaking methods is mainly based on the icebreaking levels in polar ship specifications. It is difficult to study the maximum icebreaking thickness and the speed of different icebreaking methods without classifying the icebreaking levels. The equation between the propulsion force and speed is therefore derived based on the force balance relationship. A method for judging the icebreaking method of polar ships is proposed by combining with the safety design of hull structure strength. The maximum cruising ability of the continuous icebreaking for a polar icebreaking transport ship has been determined. The reliability of the determination of the icebreaking method is verified by comparing with the model experimental results. The speed range for continuous icebreaking and impact icebreaking methods has been divided under different ice thickness conditions. It provides theoretical support for the icebreaking design and navigation of polar ships.