Aiming for the problems of large energy loss and unstable water production in multiple effect evaporation water for injection system, different preheating methods were designed to improve the water production process, and the Matlab/Simulink multi-body toolbox was used to simulate the system and optimize the thermodynamic process. According to the equations of mass and energy conservation, the mathematical models of evaporator, preheater and condenser were established with the loss of steam flow resistance. Based on the Matlab/Simulink multi-body toolbox, the iterative solution was carried out by the equal area method. The experimental data were compared with the results which were simulated by the Matlab/Simulink multi-body toolbox. The maximum error was 6.71%. Considering the waste of secondary steam energy in multiple effect evaporation system, different preheating methods were used to recover the residual heat. The influence of the number of effects and the preheating mode on the thermal performance of the system was analyzed. The results indicated that with the growth of the number of effects the specific exergy consumption decreased, specific heat transfer area and gained output ratio of the system increased, and the latter two have decreased rate of change. When the number of effects was less than 5, using the condensate preheating scheme was more excellent. When it was more than 5, using the mixture preheating scheme was superior. While the number of effects was greater in scheme mixture preheating, temperature drop and pressure drop which caused by the flow of steam rapidly rised, gained output ratio weakened and specific exergy consumption tended to be constant. This work proposed a new preheating method for the multiple effect evaporation system, which improved the utilization rate of energy in this system by recovering the residual heat of the last-effect secondary steam. The new preheating method can provide a reference for the design and transformation of the multiple effect evaporation system.