Acute respiratory distress syndrome (ARDS) is a clinical syndrome caused by intrapulmonary and/or extrapulmonary causes, characterized by intractable hypoxemia. Studies have shown that the sympathetic nervous system is over-activated in patients with acute respiratory distress syndrome. A large retrospective study showed a reduction in mortality in ARDS patients treated with oral β1 blockers before admission, and this beneficial effect of β1 blockers applies to ARDS patients with or without cardiac disease. Esmolol is an ultra-short-acting selective β1 receptor blocker. Previous studies have shown that esmolol can improve oxygenation and reduce the levels of inflammatory cytokines and exudate proteins in bronchoalveolar lavage fluid, thereby alleviating pulmonary injury. According to the literature and our previous clinical observations, we made the following hypothesis: When Estolol is applied to various ARDS patients undergoing mechanical ventilation in ICU, it can control the heart rate by inhibiting β-adrenergic receptor, which can ultimately improve the oxygenation index of patients and shorten the mechanical ventilation time. This project intends to include ARDS patients with optimal hemodynamic treatment for 24 hours, whose heart rate is still ≥95 beats/min after conventional treatment, but ≤120 beats/min. They are randomly divided into control group and Esmolol treatment group to study the effects of esmolol on patients' oxygenation index, mechanical ventilation time, hemodynamics, function of various organs and inflammation level. The aim of this study is to optimize the treatment of ARDS patients.