Under the uncertain demand environment facing both exogenous and endogenous factors, by establishing a decision model for production input, government incentives, and enterprise production scale, based on the research on the value expressions of production inputs of enterprises, the mechanism of production inputs, government incentives, and decision-making on enterprise production scale is analyzed, and the critical value equation, optimal production scale, and optimal government incentives are analyzed. The study shows: 1)Flexible enterprises can optimize the production scale according to changes in market demand, with reference to capitalized future production scale, government incentive cash flow, abandonment option value, and demand change option value, etc; 2) When the enterprise unit time income stream meets at a certain level, there exists an optimal product ion scale equation and an optimal government incentive equation and their corresponding threshold equations; 3)There is a close relationship between production input, government incentives, and enterprise production scale, and flexible enterprises can dynamically adjust production accordingly. In addition, comparisons with exogenous models verify the adaptability of the model. Therefore, it can be used as a reference to strengthen the production scale decision of enterprises in an environment of uncertain demand.