The significance and the necessity of monitoring forest fire by transmission line are introduced. Mechanisms of tripping of transmission lines caused by the fire are analyzed. The current fire monitoring methods used in transmission line are divided into two categories, one is satellite-based infra-red sensor senses hot point technology which is used for detecting macro and wide area, and the other is wireless sensor networks for early detection of forest fires which is used for local and small scope area. The current applicable principle of early warning method and corresponding algorithms are analyzed comprehensively. The advantages and shortcomings of existing early warning schemes are analyzed and compared in detail. Because of the shortage of historical data and the adverse circumstances of transmission line, we should pay more attention to the cooperation of warning models and algorithms. The unsolved problems of application of fire warning technology in the transmission line are summarized. Research on fire warning method which is more suitable for transmission lines running environment is the direction of future development.