The research and application of forest fire monitor and early-warning system for transmission line are discussed. The fundamental principle of fire monitor is introduced, and the structure and components of hardware and software of the monitor system are given. A self-adaption algorithm for fire judgment threshold is proposed to enhance the fire identification accuracy. And an optimization calculation method for the distance between fire and tower is presented to decrease the calculation amount. The developed forest fire monitor and early-warning system for transmission line is applied to the trans regional power transmission lines. Application results indicate the developed system can monitor the fire with high accuracy and publish the early-warning message, which is useful for the enhancement of resist ability of forest fire disaster for transmission lines.