Biosynthesis of caproic acid carried out reverse-β oxidation reaction by using electron donor and electron acceptors through chain elongation (CE) process. The short-chain fatty acids would be converted to high value medium-chain fatty acid (caproic with 6 carbon chains). In order to increase the production yield, the relationship between reductase and energy supply in the process of biosynthesis, the influence mechanism and appropriate range of various processing factors were discussed in this study. In this paper, the mechanism and competitive pathway of chain elongation with lactic acid and ethanol as electron donors were investigated, and the relationship between reductase and energy supply was discussed, also the electron bifurcation were considered. The influencing factors of biosynthesis of caproic acid (pH, ORP, HRT, CO2, H2 and external cathode) were summarized, and the mechanism was analyzed. The reference range and application suggestions were also provided. The bioelectrochemistry in the production of caproic acid was regarded as a promising method. The study could provide theoretical guidance for expanding the application of biosynthesis of caproic acid and improving yield.