This research contains assessment and analysis of the operation data for 30 months, analysis of 540 checklists results to determine design parameters, redesigning the WWTP to determines the problem agents and upgrading requirements, designing the various processes for upgrading and evaluating them by molt-criteria decision and selecting the most proper alternative. The results show that the main true design parameters such as BOD5 and TSS are 50 and 57 g/capita-day, respectively. The water consumption and wastewater production per capita per were 220 and 187, respectively. Using these Design criteria to come up with the best alternative for upgrading of wastewater treatment plant a number of remarks such as: ease of O and M, low operational costs, low maintenance costs, low capital costs short implementation period, potential to remove N and P, reliability of performance, innovation, pollution prevention, maximum use of facilities, long useful life and minimal plant disruptions were considered. All of the alternatives were evaluated by multi-criteria decision method. The score earned by various alternatives are: Use of rock filter in maturation pond effluent (-59), Use of micro strainers for filtration the effluent (-38), Dual powered aerated logoon (-65), Activated Sludge with digest and store excess sludge countercurrent with part of influent wastewater about 8500 m3 day-1 in available lagoons (196), Commutation of No. 1 lagoon to aeration tank and built the sedimentation tanks, invert it to extended aeration tank and use the No. 2 and 3 lagoons for sludge storing (241), Biolac Process (201), Facultative aerated lagoon in 3 modules (-107). At last the alternative with highest score was selected.