To observe the differences in the effects of different dosages of grain-sized moxibustion on uterine artery blood flow in patients with cold and dampness primary dysmenorrhea (PD). A total of 60 patients with PD were randomly divided into 3 groups with 20 cases in each group. Acupoints Sanyinjiao (SP6), Diji (SP8) and Xuehai (SP10) were selected in all the 3 groups, and different dosages of grain-sized moxibustion were used (3 moxa cones, 6 moxa cones, 9 moxa cones) respectively. Treatment started 7 days before menstruation for 3 times, lasting for a total of 3 menstrual cycles. The values of uterine artery blood flow parameters including pulsatility index (PI), resistance index (RI), and systolic/diastolic ratio (S/D) were recorded before and after treatment. The visual analog scale (VAS) score and cox menstrual symptom scale (CMSS) score (including severity [CMSS-S] and time of duration [CMSS-T]) were evaluated before treatment, at the end of each menstrual cycle, and one menstrual cycle after treatment. The values of uterine artery blood flow parameters (PI, RI, S/D) after treatment in the 9 moxa cones group were lower than those before treatment, as well as lower than those in the 3 and 6 moxa cones groups after treatment (P<0.05). The VAS scores of the 3 moxa cones group were lower than those before treatment in the first and second cycle (P<0.05). The VAS scores of the 6 and 9 moxa cones groups were lower than those before treatment at each observation point (P<0.05), and were lower than those of the 3 moxa cones group in the third cycle of treatment and follow-up period (P<0.05). And the VAS score of the 9 moxa cones group was lower than that of the 6 moxa cones group during the follow-up period (P<0.05). Compared with the scores before treatment, the CMSS-T scores at each observation point after treatment were lower in the 9 moxa cones group (P<0.05);the CMSS-T scores in the second and third cycle after treatment, and follow-up period were lower in the 6 moxa cones group (P<0.05), with the CMSS-S scores in the second and third cycle after treatment, and follow-up period lower in the 6 and 9 moxa cones groups (P<0.05). The CMSS-T and CMSS-S scores of the 6 and 9 moxa cones groups were lower than those of the 3 moxa cones group in the third cycle and follow-up period (P<0.05). The CMSS-T and CMSS-S scores of the 9 moxa cones group were lower than those of the 6 moxa cones group during the follow-up period (P<0.05). Grain-Sized moxibustion has dose-effect relationship in the treatment of PD. Compared with 3 and 6 moxa cones groups, 9 moxa cones group has advantages in improving uterine artery blood flow parameters and alleviating dysmenorrhea symptoms in PD patients.