Objective To investigate the effects of metformin and vitamin B12 of the nervous system in diabetic patients. Methods 52 cases of diabetic patients were selected as research subjects, which were 30 cases of long-term use of metformin (study group), no long-term use of metformin in 22 patients (control group), vitamin B12 levels and EMG changes in two groups were compared. Results Vitamin B12 and HDL-C levels in the observation group were significantly lower than the control group (P<0.05), HbAlC, TG, TC, no significant difference (P LDL-C levels were> 0.05). EMG normal observation group was 23.33%, significantly lower than the 50.00% in the control group, normal vibration threshold detection was 36.67%, significantly lower than the 59.09% in the control group, P<0.05. Plantar light touch to check the normal rate in both groups was 70.00% and 72.73% respectively, no significant difference between groups (P>0.05). Conclusion Metformin treatment of diabetes, may lead to reduced levels of vitamin B12, causing iatrogenic nervous system damage, metformin treatment in the application of clinical diabetes, vitamin B12 levels should be regularly monitored and replenish vitamin B12.