Objective To investigate prognosis and parameter changes of blood gas analysis in elderly patients with chronic obstructive pulmonary disease (COPD) and type Ⅱ respiratory failure. Methods Form 2013 to 2015 in our hospital, the clinical data of 85 cases of COPD in elderly patients over the age of 60 and type II respiratory failure were retrospective analysis, which were divided into improved group (66 cases) and the death group (19 cases). All of the patients were underwent arterial blood gas analysis (oxygen not before) and venous blood electrolyte determination after admission, and PH, PaCO2, and the mortality rate were compared respectively. Results (1)When blood gas analysis PH≥7.25, mortality was significantly increased. PaCO2≥80mmHg, (mortality was significantly increased, P<0.01). (2)Respiratory acidosis associated with other types of acid-base balance disorders of mortality was significantly increased (P<0.05), in particular increased when combined with other two types is more obvious (P<0.05). Conclusion (1)PH value and PaCO2 of blood gas analysis have a significant impact on the prognosis in elderly patients with COPD and type Ⅱ respiratory failure, which prognosis can be predicted to some extent. (2)The mortality rate of two or more acid-base balance disorders were higher than single one.