The invention relates to a method used for detecting hang cover type transformer winding looseness, which belongs to the technical field of power transformer safety monitoring. The method comprises the steps that 1) a hang cover type transformer with a vibration sensor is closed, and the vibration sensor and a current transformer are turned on; 2) a vibration signal and high voltage winding current are acquired; 3) a first characteristic value, a second characteristic value and a third characteristic value are acquired; and 4) looseness diagnosis is carried out on the hang cover type transformer to confirm the loose state of a winding. According to the invention, when closing is carried out, looseness judging is carried out on the winding of the transformer; compared with existing off-line detection, the winding looseness detection method provided by the invention is more timely; and the working transformer is prevented from being damaged when the winding is loose.