In this paper, we apply the Failure Modes, Effects, and Criticality Analysis (FMECA) approach to the criticality and risk analysis of the efficiency, safety/reliability, environment, and financial criteria of the high voltage transmission line. In the efficiency analysis, the weighting-scoring method and analytical hierarchy process are applied to obtain the line renovation index, which is interpreted as efficiency severity. The safety/reliability severity relates to the system impacts are caused by failure of the equipment and the system. The environmental severity takes social impacts and pollution into consideration. The financial severity involves the cost of spare parts and maintenance costs, which are interpreted as the financial severity of the lines. Twenty practical transmission lines in Thailand with actual data for 115, 230, and 500 kV were studied. The transmission line components are divided into eight components including the conductor, conductor accessories, insulator, steel structure, foundation, lightning protection system, tower accessories, and right-of-way. The severity and criticality of the components and transmission lines are analyzed and plotted in criticality matrices based on four criteria. This criticality matrix is presented at four different levels including very low, low, medium, and high risk, as represented by four color bands: green, yellow, orange, and red, respectively. The results show that three 115 kV lines are the first priority for short-term reconstruction planning because of their unacceptable condition and high risk in terms of safety/reliability and financing. Recommendations for maintenance strategy and risk mitigation are proposed for the utility according to the utility’s actual criticality. Ultimately, maintenance planning of the transmission system can be effectively managed with higher reliability, a lower risk of failure, and a lower cost of maintenance.