A syngas fed SOFC cogeneration system using a downdraft gasifier is modeled and optimized from the viewpoints of thermodynamics and thermoeconomics. A multi-objective optimization method based on genetic algorithm in the form of two different scenarios is carried out. In scenario I (exergoeconomic) the total exergy gained (TEG(CHP)) and total product unit cost (c(p)) of the system are considered as two objective functions, while in scenario II (exergoenviroment) and normalized CO2 emission (epsilon) are presumed as the two objectives. In both scenarios, optimization process is performed with the aim of maximizing the total exergy gained and minimizing the second objective function (in scenario I and in scenario II). The optimization results demonstrates that minimization of the total product unit cost of system as the only criterion leads to the higher values of normalized CO2 emission and lower values of the system exergy efficiency. In addition, it is revealed that, at the optimal conditions, despite the lower amounts of stack inlet temperature and current density for scenario II, the net electrical power obtained by scenario I is quite higher. (C) 2018 Elsevier Ltd. All rights reserved.