According to the parameter characteristics of electricity-water cogeneration power plants, an enhanced multi-stage flash (E-MSF) seawater desalination system was proposed which considered the advantage of a multiple effect distillation (MED) seawater desalination system. The main improvement ideas of E-MSF are that part of the flash vapor in flash room is extracted into the next stage to heat the flashing brine, and part or all of the inlet crude seawater was replaced by the cooling seawater of power unit. The analytical models of performance and technical economics for E-MSF were set up. Based on these models the performance and technical economics of E-MSF were analyzed and compared with MSF. The calculation results show that the gain ratio could be increased by 74.1%, the brine concentration in each stage could be reduced by 21.8% on average and the mean annual capital cost of fresh water production will decrease by 10.7% in comparison with conventional MSF when the extracting quotient of flash vapor increased to its maximum value (0.773). These improvements could make the advantages of cogeneration to be further utilized and the energy consumption of MSF will be observably reduced.