To accurately evaluate the effect of direct current（DC）voltage on oil-water interfacial tension，oil-water electrolysis experiments were conducted at 0—15 V DC voltage，taking dehydration crude oil and simulated formation water（CaCl₂ water type）of Shengli oilfield as research objects. By measuring the changes in oil-water interfacial tension，temperature and current，along with analyzing the pH value and ion content of aqueous phase，as well as the composition and functional group content of oil phase，the reduction mechanism of oil-water interfacial tension by DC voltage was explored. The results showed that with the increase of DC voltage，the interfacial tension between oil and water significantly decreased，with a maximum reduction of 42.66%. The solubility of Ca2 + in simulated formation water decreased from 2.81 mg/L to 2.25 mg/L with increasing temperature， which weakened the influence of DC voltage on oil-water interface. However，the content of Na₊ increased from 0.50 mg/L to 0.72 mg/L，which was beneficial for further reducing interfacial tension. Under the influence of electrochemical effect，the pH value of aqueous solution increased from 7.32 to 10.96. The alkaline condition promoted the reaction of acidic substances in crude oil， generating surface active substances such as carboxylic acid salts. Through infrared spectroscopy analysis，the normalized content of carboxylate was 1.40，1.51，1.90 and 4.11 at DC voltage of 0，5，10 and 15 V，respectively. The increase in carboxylate content further promoted the decrease of interfacial tension. In addition，electrochemical reactions promoted the simplification of crude oil composition. When the DC voltage increased from 0 V to 15 V，the content of asphalt and resin decreased from 18.63% and 12.96%to 12.11% and 10.06%，respectively，while that of saturated hydrocarbons increased from 47.57% to 55.89%. The research results provided theoretical support for promoting the application of DC electric fields in improving crude oil recovery efficiency.