This is a randomized,open-label study to research the changes of lung function before and after exercise in patients with chronic obstructive pulmonary disease .At baseline,lung function test,blood oxygen saturation and pulse are measured before and after 6-min walk test for each subject.Quality of life is assessed through questionnaires including modified Medical Research Council dyspnoea scale(mMRC),St George's Respiratory Questionnaire(SGRQ),Clinical Chronic Obstructive Pulmonary Questionnaire(CCQ) and chronic obstructive pulmonary assessment test(CAT).And then budesonide(160ug) and formoterol(4.5ug) bid will be given to the subjects for 3 months.The subjects will have a follow-up visit with all the examinations mentioned above after 3 months' treatment.
