Abstract: The paper studies the sensitivity of the adjustable parameters of internal-combustion engine to fuel economy with test research and model calculation methods. Based on the concept of sensitivity, the mathematical models of internal-combustion engine fuel economy and their parameter sensitivities are established. Using these models, several parameter sensitivities to internal-combustion engine fuel economy are analyzed. The sensitive characters of effecting on fuel economy of different parameters and some adjustable parameter sensitivity orders are found, and the influence of cross rule in different parameters to sensitivity is analyzed. Some considerable matters in internal-combustion engine design, transformation and application are pointed out.