The invention provides an automatic teed line parameter calculating method and a device. The automatic teed line parameter calculating method and the device are used for solving the problem that efficiency and accuracy rate are poor in calculation of parameters of a teed line in the prior art. The automatic teed line parameter calculating method includes the following steps. A starting point and a teed joint of a main line of a to-be-calculated line are obtained. Corresponding models and length of all line segments between the main line starting point to the teed joint are obtained from a production management system (PMS). Characteristic parameters of power grids corresponding to the models are confirmed. Based on the characteristic parameters of the power grids and the length, line parameters between the starting point of the main line and the teed line are calculated out and output. With the automatic teed line parameter calculating method and the device, efficiency and accuracy rate in calculating out teed line parameters are benefited and improved.