The invention discloses a flanged oil tank cover and a hot-spot temperature online monitoring method thereof, which belongs to the technical field of the design, manufacturing and signal monitoring of a transformer. The oil tank cover of the transformer is of a rectangular shape, four edges of the cover are bent towards the back surface of the oil tank cover and vertical to the plane on which the oil tank cover is arranged; the length of a bending part is greater than the length of a bolt, and joints on four corners of the bending part is smoothly welded, so that dust, rainy water and the like can be prevented from entering the oil tank; and the mechanical strength and the safety of the transformer oil tank cover can be enhanced, and the appearance of the oil tank cover is simpler and more attractive. By adopting the a soft measurement technology, a radial basis function (RBF) neural network model is built by capturing relevant information of the transformer such as real-time voltage, current, magnetic flux and leakage flux so as to realize the online monitoring of the hot-spot temperature of the transformer. The flanged oil tank cover and the hot-spot temperature online monitoring method are widely applied to an electric power system and especially to a new energy power generation system.