Considering the effects of unpredictable disturbances, a robustness criterion is newly proposed to develop an integrated evaluation with modified efficiency criterion, for comprehensive assessments of energy conversion performances in direct methanol fuel cells. The effectiveness of developed criteria in various situations (including some extreme operating conditions) has been carefully analyzed based on both experimental and numerical results. For undisturbed operations, the modified efficiency criterion could help to avoid potential misinterpretations of energy conversion process in existing criteria. For disturbed operations, the robustness criterion concerning the effects of uncertainty propagations is shown to be an effective guidance for the determination of appropriate operating current densities to design efficiency-stabilized operations. Systematic analysis on its applications in different situations proves that, the integrated efficiency and robustness evaluations can effectively differentiate the effects of operating conditions and membrane types, which is highly beneficial for one's optimal designs of stable and efficient DMFC operations.