The invention discloses an ultrasonic positioning method for partial discharge of a transformer. Ultrasonic partial discharge detection is widely applied to partial discharge defect diagnosis for the transformer. However, the internal structure of the transformer is complicated, ultrasonic waves have an obvious refraction/reflection phenomenon when passing through metal components such as an iron core and a winding, and thus the ultrasonic partial discharge positioning accuracy is enabled to be greatly reduced. According to the invention, a transformer node numerical model is built according to the structure of an entity transformer, each node in the model is endowed with a specific parameter according to ultrasonic wave propagation characteristics of a transformer component at the position where the node is located, and the propagation path of ultrasonic waves is simplified into a series of nodes arranged in sequence; meanwhile, the time of arrival of ultrasonic signals in the model is calculated by adopting a propagation duration calculation algorithm; and a partial discharge source in the transformer is positioned by adopting a particle swarm optimization algorithm on the basis of the transformer model. The ultrasonic positioning method provided by the invention for partial discharge of the transformer has very high positioning accuracy.