Corrosion is an important cause of steel pipeline failure and oil leakage, especially local pitting corrosion in long distance crude oil pipelines. Deep dehydration is of great significance to pipeline anticorrosion, however, further experimental results show that it is very difficult to achieve deep dehydration by a single electric field. Recent studies have shown that the particle size change of dispersed phase for the emulsion with large droplets after electromagnetic synergistic treatment is more obvious than that of a single electric field. In this study, the effect of micro-droplets on corrosion of oil pipelines are revealed. The role of micro-droplets in the process of microbial corrosion and electrochemical corrosion in a strong or weak acid solution for oil pipelines was summarized. A structural model of on-line tubular electromagnetic synergistic intensification coalescing device was established. The size change of particle of the dispersed phase in emulsions was studied. Crude oil and water were used as experimental materials, and the particle size distribution of dispersed phase in emulsions was tested by the evaluation system. The results showed that mean radius, d10 and d50 of water droplets in emulsion treated by electromagnetic synergism are larger than those treated by a single electric field. Strengthening droplets coalescence by electromagnetic synergism is also effective on emulsions whose particle size of the dispersed phase is less than 100μm. The role of micro-droplets in pitting corrosion is summarized based on corrosion channels. In the process of microbial corrosion and electrochemical corrosion in strong or weak acid solution, the role of water is presented in two aspects like participating in the reaction and providing ion electron transmission media. Analogous to culture medium, micro water droplets can be called corrosion medium for pitting corrosion in long-distance crude oil pipelines. A structural model of on-line tubular electromagnetic synergistic intensification coalescing device was established, including an electric field generation device and a magnetic field excitation component with orthogonal distribution and synchronous synergy. And emulsions are treated by electric and magnetic fields while flowing through the medium channel. The particle size change of dispersed phase in emulsions with average particle size of dispersed phase less than 100μm was experimental studied. It is found that mean radius, d10 and d50 of water droplets in emulsion treated by electromagnetic synergism are larger than that by a single electric field. Therefore, electromagnetic synergism can further enhance the dehydration depth compared with a single electric field.