Charge variation is one of the most important heterogeneities during monoclonal antibody (mAb) manufacturing and this study presents insights into the generation of acidic charge variants during cell culture processes. Since acidic variants generate both intracellularly and extracellularly, main charge fraction collected by weak cation exchange chromatography (WCX) was incubated in harvested cell supernatant (HCS) to simulate and investigate the extracellular process firstly. It is found that the main fraction was degraded rapidly into acidic variants rather than basic variants extracellularly, and the degradation sites were located in both Fab and Fc fragments indicated by papain digestion. Besides, certain process parameters were investigated as their potential roles in the extracellular process. As a result, media composition showed significant influence on degradation while culture time point did not, suggesting that the extracellular process was a spontaneous process without enzyme catalysis. Additionally, kinetics study reveals that the extracellular process was a pseudo first-order reaction. The E (app) value (21.59 kcal/mol) estimated from the Arrhenius equation suggests that the extracellular degradation might be mainly attributed to asparagine deamidation. Furthermore, we established an acidic variants generation model, indicating that the extracellular process plays a dominant role in modulating the final acidic variant level. This study provides better understanding for controlling product heterogeneity in mAb manufacturing.