Objective To explore the characteristics and influencing factors of cognitive function among middleaged inpatients with Obstructive Sleep Apneahypopnea Syndrome (OSAHS). Methods Totally 348 middleaged OSAHS inpatients were recruited using convenience sampling, then Montreal Cognitive Assessment Scale (MoCA) was utilized to assess their cognitive function, and the patients were divided into a cognitive normal group and a cognitive impairment group according to their MoCA score, the characteristics of cognitive function among middleaged OSAHS inpatients were analyzed comparatively, and its influencing factors were determined using multivariate logistic regression analysis. Results The incidence of cognitive impairment was 39.66% in middleaged OSAHS inpatients. There were significant differences in delayed recall and attention between the two groups (P<0.01 for both). Logistic regression analysis revealed that, age, educational background, frequency of physical exercise and mean oxygen saturation were the influencing factors of cognitive impairment in middleaged OSAHS inpatients(P<0.01 for all). Conclusion Cognitive impairment is serious in middleaged OSAHS inpatients, especially in the area of delayed recall and attention. And cognitive impairment has something to do with patients′ older age, lower educational background, inadequate physical exercise and low oxygen saturation.