Abstract: Objective To investigate the value of diagnosis and differential diagnosis of pulmonary function indexes in the elderly with chronic obstructive pulmonary disease (COPD) and the elderly with coronary heart disease (CHD). Methods from March 2015 to March 2017, 60 patients with CODP and 60 patients with CHD were selected as COPD group and CHD group respectively, and 60 healthy subjects were selected as control group. Using Masterscreen PFT pulmonary function instrument, the routine pulmonary ventilation, pulmonary diffusion function and pulmonary volume were measured in all subjects. Results levels of vital capacity (VC), forced vital capacity (FVC), forced expiratory volume in one second (FEV1), FEV1/FVC, peak expiratory flow (PEF), diffusion capacity of the lung for carbon monoxide (DLCO) and DLCO/alveolar volume (DLCO/VA) in COPD group and CHD group were significantly lower than those in the control group (P<0.01). The levels offunctional residual capacity (FRC), residual volume (RV) and RV/total lung capacity (RV/TLC) in COPD group and CHD group were significantly higher than those in the control group (P<0.01), and COPD group were significantly higher than those in CHD group (P<0.01). Conclusions The detection of pulmonary function index can effectively diagnose and differentiate COPD and CHD in the elderly, which has an important guiding role in early diagnosis and treatment of COPD and CHD, and is worthy of clinical promotion.