Objective  To study the effect of HMB on postoperative patients with lower extremity fracture and malnutrition. Methods  From February 2016 to August 2017, 84 patients with lower limb fracture and malnutrition in affiliated hospital of Hebei university of engineering were selected as the subjects. They were divided into a study group and a control group by random number table. The control group was given with 2013 version of Chinese annual dietary nutrient intake to provide dietary intervention. The study group was treated with HMB (1 packet/time, 2 times/d, 20 g/d) on the basis of the control group. The patients in both groups were treated for 3 months. TP, Hb and ALB levels and other nutritional indicators were compared between the two groups before and after intervention. Using Inbody 720 muscle diagnostic instrument detect and compare the muscle volume of two groups before and after intervention. The incidence of postoperative complications and satisfaction were compared. Results  There was no significant difference in nutritional index level between two groups before intervention (P>0.05). After the intervention, the study group of TP, Hb, ALB level was (65.12±4.90)g/L, (114.30±8.29)g/L and (31.59±3.17)g/L respectively, which were significantly higher than the control group of (50.39±6.24)g/L, (106.26±7.15)g/L and (26.15±3.47)g/L, differences between groups were statistically significant (P<0.05). There was no signifcant difference in  limbs muscle tissue level between two groups before intervention (P>0.05), After the intervention, the study group of limbs muscle tissue level was (24.39±2.76) kg, which was signifcantly higher than level before intervention of (20.87±2.50)kg, the limbs muscle tissue level of control group after  intervention was (24.39±2.76), which was not signifcantly higher than level before intervention of (20.76±2.51)kg (P>0.05), the limbs muscle tissue level of study group after  intervention was was signifcantly higher than level of control group (P<0.05). The study group of postoperative pulmonary infection and fracture healing, muscle weakness, muscle atrophy rate were 2.38% (1/42), 2.38% (1/42), 0.00% (0/42), 0.00% (0/42), which were significantly lower than the control group of 19.05% (8/42), 16.67% (7/42), 11.90% (5/42), 9.52% (4/42), differences between groups were statistically significant (P<0.05). The satisfaction of study group was 95.24% (40/42), which was significantly higher than 80.95% (34/42) of the control group, and the difference between groups was statistically significant (P<0.05). Conclusions  HMB used in lower limb fractures associated with poor nutrition in postoperative patients can improve the nutritional status, increase the limb muscle tissue level, at the same time effectively reduce the incidence of postoperative complications, improve patients’ satisfaction.