OBJECTIVE： To investigate the formulation of therapy plan and pharmaceutical care for a penicillin allergic patient with necrotizing fasciitis combined with diabetes mellitus. METHODS： A penicillin allergic patient with necrotizing fasciitis combined with diabetes mellitus was admitted to Ordos central hospital on March 30， 2018. According to the disease characteristics of the patient， clinical pharmacists conducted pharmaceutical care during the treatment process from the aspects of antiinfective drugs selection， monitoring points of necrotizing fasciitis， blood glucose monitoring， effects of hypoproteinemia on antibiotic pharmacokinetics-pharmacodynamics， and assisted the physician to develop a more reasonable and effective individualized therapentic regimen. RESULTS： For diabetes mellitus， the patient adjusted Insulin lispro injection （insulin pump）， Acarbose tablets， Metformin hydrochloride tablets and Glimepiride tablets successively. For rapid atrial fibrillation with intraventricular differential conduction and ST-T changes， Metoprolol tartrate tablets were used to reduce heart rate. For necrotizing fasciitis， when choosing drugs to ensure the anti-infective effect， considering that the patient had penicillin allergic and hypoproteinemia， clinical pharmacists chose drugs with low protein binding rates and different from the mother nucleus and side chain of penicillin. Imipenem cilastatin for injection， Aztreonam for injection， Levofloxacin lactate and sodium chloride injection were used successively. Voriconazole for injection was adopted for anti-fungal treatment. Physicians adopted the suggestions of clinical pharmacists. Debridement through early thorough drainage and rational drug use， the patient’s condition was effectively controlled. CONCLUSIONS： Clinical pharmacists assist physicians to formulate and optimize whole course therapentic regimen so as to improve the safety and effectiveness of drug treatment.