A ceramic membrane micro-extractor (CME), employed for continuous re-extraction of penicillin G (PEN G), was studied systematically. The droplet size was investigated in the re-extraction process. Re-extraction efficiency (RE) and degradation rate of PEN G were extensively examined by superficial Reynolds number (Reh), phase ratio (R), initial PEN G concentration and membrane pore size. To further understand and quantitatively analyze the re-extraction behavior, resistance-in-series (RIS) model was developed to predict the re-extraction efficiency at steady-state conditions. First of all, a three-parameter correlation was defined for quantitative description of droplet size. The main factors affecting the re-extraction efficiency of PEN G were superficial Reynolds number and phase ratio. The re-extraction efficiency of PEN G reached 99% or above at Reh > 934 and R > 0.08. Meanwhile, the degradation rate of PEN G (D) decreased to 0.5% when Reh was 934. Compared with the re-extraction performance of the batch extractor, less residence time was needed and the degradation rate decreased 50%. The theoretical re-extraction efficiency (RET) was in good agreement with the experimental data.