Objective To investigate the effectiveness of autologous nano-fat mixed granule fat transplantation in the treatment of facial soft tissue dysplasia in children with mild hemifacial microsomia (HFM). Methods A total of 24 children with Pruzansky-Kaban type Ⅰ HFM were admitted between July 2016 and December 2020. Among them, 12 children were treated with autologous nano-fat mixed granule fat (1∶1) transplantation as study group and 12 with autologous granule fat transplantation as control group. There was no significant difference in gender, age, and affected side between groups (P>0.05). The child’s face was divided into region Ⅰ(mental point-mandibular angle-oral angle), region Ⅱ (mandibular angle-earlobe-lateral border of the nasal alar-oral angle), region Ⅲ (earlobe-lateral border of the nasal alar-inner canthus-foot of ear wheel). Based on the preoperative maxillofacial CT scan+three-dimensional reconstruction data, the differences of soft tissue volume between the healthy and affected sides in the 3 regions were calculated by Mimics software to determine the amount of autologous fat extraction or grafting. The distances between mandibular angle and oral angle (mandibular angle-oral angle), between mandibular angle and outer canthus (mandibular angle-outer canthus), and between earlobe and lateral border of the nasal alar (earlobe-lateral border of the nasal alar), and the soft tissue volumes in regions Ⅰ, Ⅱ, and Ⅲ of healthy and affected sides were measured at 1 day before operation and 1 year after operation. The differences between healthy and affected sides of the above indicators were calculated as the evaluation indexes for statistical analysis. At 1 year after operation, the parents, the surgeons, and the nurses in the operation group made a self-assessment of satisfaction according to the frontal photos of the children before and after operation. Results The study group and the control group were injected with (28.61±8.59) and (29.33±8.08) mL of fat respectively, with no significant difference (t=0.204, P=0.840). After injection, 1 child in the control group had a little subcutaneous induration, and no related complications occurred in the others. All children in both groups were followed up 1 year to 1 year and 6 months, with an average of 1 year and 4 months in the study group and 1 year and 3 months in the control group. At 1 year after operation, the asymmetry of the healthy and affected sides improved in both groups; the satisfactions of parents, surgeons, and nurses in the study group were all 100% (12/12), while those of the control group were 100% (12/12), 83% (10/12), and 92% (11/12), respectively. The differences between healthy and affected sides in mandibular angle-oral angle, mandibular angle-outer canthus, earlobe-lateral border of the nasal alar, and the soft tissue volume in 3 regions of the two groups after operation were significantly smaller than those before operation (P<0.05). There was no significant difference in the above indexes between the two groups before operation (P>0.05). After operation, all indexes were significantly lower in study group than in control group (P<0.05). Conclusion Autologous nano-fat mixed granule fat transplantation and autologous granule fat transplantation can both improve the facial soft tissue dysplasia in children with mild HFM, and the former is better than the latter.