Objective To investigate the difference in clinical features and chest HRCT findings between idiopathic nonspecific interstitial pneumonia(INSIP)and connective tissue disease-associated nonspecific interstitial pneumonia(CTD-NISP). Methods Totally 73 cases of NISP from 2011 to 2016 were retrospectively reviewed ,whose final diagnosis all were made after clinico-radiologic-pathologic discussion and 52 cases of them were diag-nosed as INSIP and 21 cases as CTD-NSIP. Clinical features ,lung function test results and chest HRCT findings of INSIP and CTD-NSIP were compared. Results Common underlying diseases of CTD-NSIP were poly-/dermato-myositis(PM/DM),rheumatoid arthritis(RA)and Sjogren syndrome(SS). The mean age of CTD-NSIP[(47.14 ± 9.24)y]was younger than that of INSIP[(59.09 ± 11.20)y](P<0.05). Compared to CTD-NSIP,expectoration was more common in patients with INSIP,while dry mouth/eyes,arthralgia and erythra were less common in INSIP (P < 0.05). Lung function test1 showed restrictive ventilatory dysfunction with dispersion function decline was found in both groups. There were no significant differences in lung function test results between INSIP and CTD-NSIP. In HRCT,the subpleural vertical line was more common in INSIP than that in CTD-NSIP,while patchy consolidation,subpleural curvilinear shadow,pleural effusion and esophageal dilation were less common in INSIP(P<0.05). Conclusions Specific difference of clinical and HRCT features between CTD-NSIP and INSIP are conducive to differentiating the two from each other.