Above 98% of the Ethiopian electric power transmission types are Over Head transmission line (OHTL) which are an outdoor system. In addition to load variation and Generation change, OHTL sag, tension, and conductor length variation due to weather fluctuation are also other problems for reliable power delivery. Without reliable power delivery, power generation is just simply a waste of resources. Mostly Ethiopian Electric power system delivery is interrupted because of OHTL failure by different factors. It can be easily affected by weather changes such as variation of temperature due to thermal expansion and elastic elongation. Additionally, the horizontal wind pressure and vertical ice loading make the value of sag, tension, and conductor length vary in a range of values. Such changes make the calculated data uncertain and require analysis of OHTL parameters with uncertainty. The temperature and conductor length variation affects the resistance of OHTL. This variation leads to voltage drop and power loss, which is mostly considered as load variation and other disturbances. To calculate resultant weight, sag, tension, cable length, and resistance of an OHTL, Interval Arithmetic (IA) and Monte Carlo (MC) approaches based on uncertainty concept for a catenary curve is proposed. The results based on the two methods are compared and analyzed with 400kV OHTL from Bahir Dar to Addis Abeba of the case study area. From 10 cities the worst affected is Addis Ababa city with the uncertain results of resultant weight varies from the minimum 21.1912 kg/m to 27.7765 kg/m, the tension changes from 10685.87 N to 9893.24 N, the sag and conductor length changes from the minimum 2.7935 m and 123.5112 m to 6.0759 m and 124.1431 m, respectively. Also, the least affected is Bura city varies from the minimum 21.0814 kg/m to 21.4765 kg/m, the tension changes from 9950.6208 N to 9671.7312 N, the sag and conductor length changes from the minimum 3.5195 m and 123.6103 m to 3.6772 m, and 123.6348 m, respectively. The IA based result gives a more conservative bound than the MC method in all the cases.