The invention discloses a culturing method of a clostridium strain YB-7 for anaerobically degrading oil-field wastewater. The method comprises the steps of after diluting activated sludge in a gradient manner, selecting bacteria solution with concentration of 10<6>-10<8>, coating the bacteria solution into a reinforced clostridium medium by using a spread plate method, and placing the reinforced clostridium medium into an anaerobic incubator for performing isolated culturing or 7 days at the temperature of 37 DEG C; and then selecting single colonies with good growth trends and different shapes from the reinforced clostridium medium, inoculating the single colonies into the new reinforced clostridium medium by using a streak culturing method, then placing the new reinforced clostridium medium into the anaerobic incubator for culturing for 7 days at the temperature of 37 DEG C, and thus acquiring the clostridium strain by screening, wherein the bacterial colony is white, with irregular shape, smooth surface, non-transparent body and irregular edge, and is named YB-7, and then respectively performing purification culturing on the YB-7 for three times, thus acquiring the pure clostridium strain YB-7 without being interfered by other unwanted bacteria. The clostridium strain YB-7 cultured according to the method provided by the invention has good anaerobic degradation effect on the oil-field wastewater, and is convenient for popularization to use.