Abstract： Objective To analyze the value of automated acid-base mapping on diagnose and treatment of patients with community acquired pneumonia (CAP) in emergency department.Methods According to medical history,pulmonary function test,diagnosing guideline of chronic obstructive pulmonary disease (COPD),111 patients with CAP were divided into two groups:single CAP group (n=56) and COPD complicated with CAP group [acute exacerbation of chronic obstructive pulmonary disease (AECOPD) group,n =55].After enquiring medical history,arterial blood samples were drawn for blood gas analysis and automated acid-base mapping was analyzed.Results Arterial blood gas analysis showed arterial carbondioxide partial pressure (PaCO2,kPa),HC03- (mmol/L),base excess (BE,mmol/L) of AECOPD group were obviously higher than those in CAP group (PaCO2:7.714 ± 2.414 vs.5.896 ±1.308,HCO3-:30.767 ± 7.185 vs.25.014 ± 3.043,BE:4.345 ± 5.371 vs.-0.354 ± 3.180,all P＜0.01 ).Automated acid-base mapping showed acid-base disturbance of AECOPD group was 89.1％ and CAP group was 66.1％.Chi-square analysis were done for patients of normal ( 10.9％,33.9％),acute respiratory acidosis (12.7％,14.3％ ),chronic respiratory acidosis (49.1％,10.7％),respiratory alkalosis (7.3％,14.3％),metabolic acidosis ( 12.7％,17.9％),metabolic alkalosis ( 12.7％,8.9％) between AECOPD group and CAP group,and statistical significance was found between AECOPD group and single CAP group ( x2=24.421,P=0.001 ).Advanced Chi-square analysis for patients of normal,acute respiratory acidosis,respiratory alkalosis,metabolic acidosis,metabolic alkalosis were done and showed no statistical difference ( x2=5.280,P=0.260).It is indicated chronic respiratory acidosis occurrences rate in AECOPD patients was higher than single CAP patients.Conclusions Our study demonstated that automated acid-base mapping may be helpful for emergency physician to rapidly recognize multi-acid-base disturbance in patients with CAP,and to promptly indentify acute or chronic phase of respiratory disease.