This study compared the effects of Curcuma longa before and after processing with vinegar on the rat model of dysmenorrhea with the syndrome of liver depression and Qi stagnation to reveal the mechanism of vinegar processing in improving the role of C. longa in soothing liver and relieving pain. The rat model of dysmenorrhea with the syndrome of liver depression and Qi stagnation was established according to the Preparation of the Animal Model of Dysmenorrhea(Draft) and the chronic unpredictable stress me-thod. The changes in the body weight, organ indexes, writhing latency, writhing score, and serum levels of six liver function indicators, sex hormones, pain factors, and blood rheological indicators were measured to evaluate the efficacy of C. longa processed with vinegar or not in treating dysmenorrhea in the rats with syndrome of liver depression and qi stagnation. Compared with the model group, the C. longa group(processed with vinegar or not) showed slow weight loss, increase in writhing latency, and decrease in writhing response(P<0.05). The inhibition rates on writhing in raw C. longa, vinegar-processed C. longa, and positive groups were 33.780%, 64.611%, and 62.466%, respectively. The significantly higher inhibition rate of the vinegar processing group indicated that vinegar-processed C. longa demonstrated more significant therapeutic effect. The vinegar-processed C. longa group showed lower levels of alanine aminotransferase(ALT), alkaline phosphatase(ALP), aspartate aminotransferase(AST), direct bilirubin(DBIL), and total bilirubin(TBIL) and higher level of albumin(ALB)(P<0.05), which indicated that vinegar processing enhanced the therapeutic effect of C. longa on liver injury. The serum levels of estradiol(E_2) and oxytocin(OT) were lower in the vinegar-processed C. longa group(P<0.05), indicating that the vinegar-processed C. longa could regulate the sex hormone levels, reduce the activity of uterine smooth muscle and contraction of uterus, and alleviate the symptoms of dysmenorrhea in rats. Moreover, the vinegar-processed C. longa group showed lower interleukin-6(IL-6) and arginine vasopressin(AVP) levels and higher beta-endorphin(β-EP) level(P<0.05), which indicated that vinegar-processed C. longa regulated the levels of pain factors to exert the pain-relieving effect. Drug intervention decreased the whole blood viscosity low-cut, medium-cut and high-cut values, plasma viscosity, whole blood reduction viscosity low-cut and high-cut values, erythrocyte cumulative pressure, and equation K value of erythrocyte sedimentation rate(P<0.05), and the vinegar-processed C. longa group outperformed other groups. This result indicated that vinegar processing enhanced the function of C. longa in improving the local blood rheology. C. longa processed with vinegar can enter the liver to relieve the da-mage to the heart, liver, kidney, and uterus, repair the liver function, and recover the sex hormone levels and immune function by regulating the levels of sex hormones and pain factors and improving the blood rheology. It activates the pain-relieving mechanism to relieve the pain, protect the liver, and fight inflammation, which is consistent with the theory that vinegar processing facilitates C. longa entering the liver to sooth liver and relieve pain.