This paper studies power and voltage control of 115kV central-I area transmission network in Lao PDR by using the Excel's solver to calculate power flow. Many commercial power flow programs are presently available. The well-known Excel worksheet comes with a solver feature in which optimization of a function with many variables can be performed. Hence, the Excel's solver can be used to calculate power flow. In addition, it will provide opportunities to improve calculation methods as well as to improve understanding of power systems. Therefore, in this paper, Excel's solver is used to calculate optimal power flow, increase the voltage profile to the base rate with install capacitor banks at some substations which voltage drop below certain value. The solutions from Excel's solver compared with commercial power flow program such as Power World are discussed. © 2004 IEEE.