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To improve the production effect of oil-water transitional zone in thin-shallow extra heavy oil reservoirs of Chunfeng Oilfield in western marginal area of the Junggar Basin, microbial enhanced oil recovery was studied taking the P6-P48 well of the oil-water transitional zone as an example. In the early stage of steam stimulation, the P6-P48 well was shut-in due to high water cut caused by edge water incursion, and analysis showed that its reservoir conditions are suitable for microbial cold production technology. According to the P6-P48 well oil sample composition, the study screened indigenous microbe strain of bacillus XJ2-1, aeruginosa XJ3-1, Dietz's bacteria Z4M8-2, inoculating microbes strain of bacillus SLG5B10-17, nutrient solution, and activator; and designed microbial injection scheme according to near borehole zones treatment radius. In September 2014, 865 m3 of microbial bacterial liquid, nutrient solution and activator was injected and the well was shut in for 166 d of reaction time. The well-hole was opened to produce in March 15, 2015, and has produced 405 d until April 30, 2016, producing oil 3 464 t. The 50 °C degassing crude oil viscosity was decreased by 58% after microbial enhanced oil recovery, and the injected live bacteria was found in produced fluid, with more quantity, indicating that the injected bacteria are adaptive and has reproduced in formation condition. Compared with 16 adjacent wells of steam soaking, microbial enhanced oil recovery has long valid period and better economic benefit. Microbial enhanced oil recovery also got good results in the P6-P49 and P6-P47 wells. Key words: oil-water transitional zone, extra heavy oil reservoir, microbial enhanced oil recovery, economic benefit, Chunfeng oilfield, Junggar Basin