The invention provides an optimization method for determining a flue gas excess heat organic Rankine cycle system parameter. The optimization method comprises the steps of taking into account of a cooling water cycle to establish a thermodynamic model; through a first law of thermodynamics and a second law of thermodynamics, obtaining system net output power, water pump waste power, heat efficiency, (the formula is shown in the description) efficiency and irreversible loss, and according to the influence of an evaporation temperature and an expansion ratio on system thermodynamic performance, determining an optimal evaporation temperature; under the optimal evaporation temperature, calculating heat exchange areas of an evaporator and a condenser, wherein it is defined that an economical objective function is the ratio of the system net output power to the area of the evaporator to the area of the condenser, and the comprehensively evaluation function is the weighted sum the economical objective function (the formula is shown in the description) and the efficiency; with the comprehensive evaluation function being an optimization target, determining an optimal condensation temperature; according to the optimal evaporation temperature and the optimal condensation temperature, determining system parameters of work medium mass, cooling water mass, evaporation pressure, condensation pressure, an expansion ratio, the net output power, the heat efficiency and the irreversible loss. According to the optimization method for determining the flue gas excess heat organic Rankine cycle system parameter, the optimal evaporation temperature and the condensation temperature can be determined, and thus the optimal system parameter is determined.