Abstract: Rapid changes of river hydrodynamic conditions in cold regions can often lead to a mechanical breakup of river ice cover(known as" Wu Kai He" in Chinese)during winters or early springs.The formed ice ja s and dams on rivers result in a great danger to the public,causing the rise in water level and ice flooding.In this study,the mechanism of mechan ical breakup of river ice cover is investigated.The criterion for determining the mechanical breakup of river ice cover is proposed using a hydrothermal method.The criterion is validated using the field measurement from the Hequ reach of the Yellow River.The result shows that the ice breakup fo recast using the criterion is in good agreement with the observation.