Abstract: To better understand the metabolism in industrial lactic acid fermentation by Bacillus coagulans, the lactic acid fermentation characteristics with mixed carbon sources were studied under varied aeration, pH, and neutralizer conditions in laboratory-scale bioreactor, and the effects of metal ions and osmotic pressure on the autolysis of B. coagulans under starvation were conducted. The results showed that the lactic acid fermentation by B. coagulans using glucose+trehalose as the mixed carbon source showed a significant carbon catabolite repression (CCR), and the fermentation process could be divided into glucose consumption phase (phase I), organic acids consumption phase (phase II) and trehalose consumption phase (phase III). Differents fermentation conditions had less of an impact on cell growth and lactic acid production at phase I, but had a considerable impact on phase III. In the phase III, the highest trehalose consumption rate and lactic acid productivity appeared at 7.2 L/h (0.03 vvm) ventilation. The rates of sugar consumption and lactic acid production were higher at pH6.5 than that at pH6.0, while nearly no trehalose consumption and lactic acid production were observed at pH5.5. Compared with NaOH, when Ca(OH)₂ was used as a neutralizer at pH6.5, the trehalose utilization rate and lactic acid production rate were enhanced by 21.0% and 28.3%, respectively. It was found that Ca²⁺ and Mg²⁺ alleviated autolysis, while Na⁺ had some benefits in maintaining the activity of cells. The results of this paper would lay the foundation for studying the mechanism of metabolic shift during lactic acid fermentation by B. coagulans in mixed carbon sources.