Objective The purpose of this study was to observe the dynamic indexes of respiratory mechanics in patients with continuous airway monitoring,and to monitor the Bispectral index （BIS） and the Observer's Assessment of Alertness/Sedation Scale （OAA/S）. We evaluated the effect of dexmedetomidine （Dex） on the autonomic respiratory function and the sedative depth of the patients in a comprehensive and systematic way,so as to provide reference for the clinical safety of Dex. Methods In the study,we randomly divided 80 patients into four groups,Dex 0.5,group g/kg （group D₁）,1 group g/kg （group D₂）,1.5 g/kg group （D₃ group） and control group （D₀ group）. There were 20 cases in each group. At about 35min before anesthesia induction,Dex or 0.9% saline 10 mL was injected intravenously. The following time points were selected： pre- administration （T0）,pre-treated 5min （T1）,pre-treated 10min （T2）,pre-processed 15min （T3）,pre-processed 20min （T4）,pre -treated 25min （T5） and pre-treated 30min. The following experimental parameters were recorded at the above time point： tidal volume （VT）,minute ventilation （MV）,end expiratory carbon dioxide partial pressure （P_ETCO₂）,respiratory frequency （RR）,first second exhalation rate （FEV1%）,compliance ring （PV ring）,resistance ring （FV ring）,pulse oxygen saturation （SpO₂）,heart rate （HR）,and respiratory mechanics parameters and circulatory parameters such as mean arterial pressure （MAP）,bispectral index （BIS） and vigilance / sedation score （OAA/S）. At the same time at T0,T1,T3 and T6,arterial blood gas was extracted,and PaO₂,PaCO₂ and pH values were recorded. Results Compared with the control group,the value of VT,RR,MV,PETCO₂,FEV1%,PaCO₂ and SpO₂ in group D₁ did not change significantly （P>0.05）,and the morphology of PV ring and FV ring were basically normal. In group D₂ and group D₃,MV decreased by 16.9% and 27% respectively;PaCO₂ increased by 11% and 19.9% respectively;FEV1% decreased by 11% and 14.9% respectively. No apnea occurred in the four groups,and all patients had SpO₂ at 98% or above. The area of PV rings and FV rings of spontaneous breathing in group D₃ was reduced （P<0.05）. The BIS values in group D₁ were above 85,OAA/S 4 was 65%,sedative satisfaction rate was low,20% patients had a score of 3 in OAA/S;group D₂ had the highest sedative satisfaction rate,70% of patients had a score of 3 in OAA/S,and no excessive sedation;60% of patients in group D₃ with an OAA/S score that was less than or equal to 2. Conclusion The sedation effect that was caused by intravenous infusion of Dex and its effect on respiratory mechanics are as follows： with the increase of Dex's dose,the degree of sedation is deepened. Although SpO₂ is still in the normal range,the respiration will be restrained （the area of PV ring and FV ring is narrowed,the value of PaCO₂ is increased）,and the clinical recommendation of intravenous infusion Dex is at a dose of 0.5µg /kg~1µg /kg for safety reasons. .