This thesis is focused on developing power flow solver based on Matlab tools. The solver is used to investigate the steady state of transmission network under different cases of demand variation. The solver is designed to be flexible and able to handle standard data format for exchanging input and output with other software tools. The active power dispatch can be solved based on three mode Conventional , Op- timal and Droop Control. The solver setting and case parameters are organized in single structure to be flexible for configuration and easy for exchange. New data file format is proposed to encapsulate the all case information in single file. The solver is implemented to solve multiple case of demand variation by single call which to automate the analysis process and minimize to iteration time. The mathematical equation model can be selected to be based on conventional admittance matrix or in- cident matrix methods. The solver results of IEEE test cases have been verified with alternative commercial and scientific tools and they satisfied the required accuracy and performance. The solver is released as open source project to support additional functionality and full customization for scientific research.