In order to obtain oil-based drilling fluids with stable performance at low oil to water ratios，the stability of water-in-oil emulsions is critical. The effects of emulsifier addition，organic soil addition and temperature on the stability of water- in- oil emulsion with oil-water ratio of 60/40 were analyzed by electrical stability test，static stability test and micro-morphometry. The results showed that when the addition of the emulsifier was 4% ，the emulsion droplets were fine and dispersed evenly，the demulsification voltage was the highest and the emulsion stability was the best. At the temperature of 100 ℃ and 120 ℃，the emulsion droplet size changed little，and the demulsification voltage was close，indicating that there was little difference on stability. However，when the temperature increased up to 150 ℃，the emulsion droplets augmented significantly，the demulsification voltage droped sharply，stability significantly deteriorated. When adding 2% organic soil，the emulsion droplets under 400 times objective lens were invisible to the naked eye，the demulsification voltage exceeded 400 V，and the oil separation rate was only 0.1% after standing for 25 hours，as a result，the stability was remarkably improved. Analyzing the mechanism of key materials and optimizing the amount of appropriate treatment agent were important to ensuring the stability of emulsions with low oil-to-water ratio，which had practical guiding significance for on-site oil-based drilling fluid performance maintenance.