Objectives: Many studies have suggested the effectiveness of single control measures in the containment and mitigation of pandemic influenza A (H1N1) 2009. The effects of combined interventions by multiple control measures in reducing the impact of an influenza A (H1N1) 2009 outbreak in a closed physical training camp in Beijing, China were evaluated. Methods: Oseltamivir was prescribed for the treatment of confirmed cases and possible cases and as prophylaxis for all other participants in this training camp. Public health control measures were applied simultaneously, including the isolation of patients and possible cases, personal protection and hygiene, and social distancing measures. Symptom surveillance of all participants was initiated, and the actual attack rate was calculated. For comparison, the theoretical attack rate for this outbreak was projected using the Newton–Raphson numerical method. Results: A total of 3256 persons were present at the physical training camp. During the outbreak, 405 (68.3%) possible cases and 26 (4.4%) confirmed cases were reported before the intervention and completed oseltamivir treatment; 162 (27.3%) possible cases were reported after the intervention and received part treatment and part prophylaxis. The other 2663 participants completed oseltamivir prophylaxis. Of the possible cases, 181 with fever ≥38.5 °C were isolated. The actual attack rate for this outbreak of pandemic influenza A (H1N1) 2009 was 18.2%, which is much lower than the theoretical attack rate of 80% projected. Conclusions: Combined interventions of large-scale antiviral ring prophylaxis and treatment and public health control measures could be applied to reduce the magnitude of influenza A (H1N1) 2009 outbreaks in closed settings.