Design and Economic evaluation of high voltage transmission line is a complicated process.This paper presents the design process of a 765 KV 100 km long Moheshkhal - Madunaghat transmision line .This study investigates the power transfer capability, line parameters, locational marginal price, and losses.These values are based on analytical methods. A six-bundule conductor model is developed using 30 - 60 - 90 triangle properties. AC optimal power flow is used to validate a three bus test system and evaluate the techno-economic benefits of the 765 KV transmission line. The system load forecast is built based on GDP elasticity method. Two types of conductors ,a cardinal and a tern, are used. The results show that compared to the hexa bundle tern conductor, the bundle of six cardinal ACSR conductor is better for a propesed transmission line. The conductor surface gradient is permissible limit to suppress the audiable noise. Several plausible case studies are examined.The study indicates enhancing the Matarbari- Madughat 400 KV line to 765 KV after 2035.