The model-based profit optimization for baker's yeast fed-batch fermentation was done in this paper. The model system used for simulation was a combined metabolic and cell cyclic model for baker's yeast Saccharomyces cerevisiae. The objective function was built according to cost-effect balances, while the required data came from a baker's yeast factory. The simulation of profit optimization revealed that in order to obtain the highest profit, there exist optimal operation regions for major manipulating variables, such as substrate feeding rate, sugar concentration in feed, aeration rate and fermentation period.