The invention provides a scissor-type self-expansion spanning system for power transmission line live stringing. The scissor-type self-expansion spanning system includes two groups of oppositely expanding scissor-type self-expansion spanning racks arranged at the two sides of a highway and an electric railway, and a wing support for carrying leads is arranged between the two groups of scissor-type self-expansion spanning racks. The system is characterized by being simple in structure, convenient to implement, and flexible in combination, preventing the limitation of span stringing due to traffic closure, saving the cost for a large amount of span erection, reducing the span construction difficulty and improving the safety and reliably of span construction.