Combination therapy with pegylated interferon (PEG-IFN) and nucleos(t)ide analogues (NAs) can enhance hepatitis B surface antigen (HBsAg) clearance. However, the specific treatment strategy and the patients who would benefit the most are unclear. Therefore, we assessed the HBsAg loss rate of add-on PEG-IFN and explored the factors associated with HBsAg loss in chronic hepatitis B (CHB) patients. This was a real-world cohort study of adults with CHB. Hepatitis B e antigen (HBeAg)-negative NAs-treated patients with baseline HBsAg <= 1500 IU/ml and HBV DNA < the lower limit of detection, or 100 IU/ml, received 48 weeks of add-on PEG-IFN. The primary outcome of the study was the rate of HBsAg loss at 48 weeks of combination treatment. Using multivariable logistic regression analysis, we determined factors associated with HBsAg loss. HBsAg loss in 2579 patients (mean age: 41.2 years; 80.9% male) was 36.7% (947 patients) at 48 weeks. HBsAg loss was highest in patients from south-central and southwestern China (40.0%). Factors independently associated with HBsAg loss included: increasing age (odds ratio = 0.961); being male (0.543); baseline HBsAg level (0.216); HBsAg decrease at 12 weeks (between 0.5 and 1.0 log(10) IU/ml [2.405] and >1.0 log(10) IU/ml [7.370]); alanine aminotransferase (ALT) increase at 12 weeks (1.365); haemoglobin (HGB) decrease at 12 weeks (1.558). There was no difference in the primary outcomes associated with the combination regimen. In conclusion, HBsAg loss by combination therapy was higher in patients from southern China than those from the north. An increased chance of HBsAg loss was associated with baseline characteristics and dynamic changes in clinical indicators.