As a new type of operation and maintenance mode for transmission lines, helicopter patrol inspection has the advantages of high efficiency, good effect, etc. However, its large-scale application should be based on the premise of safety operation. In this paper, a safety risk assessment model of helicopter inspection is established by using risk matrix, in which the safety risk factors of the whole operation process are analyzed from the aspects of personnel, equipment and environment. The risk value is determined by the risk probability and the consequence severity, and then the risk level of each risk factor can be assessed according to the position of the risk value in the risk matrix. Differentiated risk control measures are proposed to avoid high-risk operations and provide a favorable support to ensure the safety of power grid, operating personnels and equipment.