Abstract: Objective: To probe into the relations between the severity of obstructive sleep apnea-hypopnea syndrome(OSAHS) and the body mass index,daytime lung function and blood gas analysis.Methods: Thirty-eight subjects who were diagnosed as sleep apnea-hypopnea syndrome by polysomnography(PSG) were studied.Their lung functions,blood gas analysis in the daytime were measured.Results: The sleep architecture changes,the increase of sleep shift number and total arousal number were significantly correlated to the degree of OSAHS.The daytime lung functions and blood gas analysis were not correlated to the degree of OSAHS.But the daytime arterial blood oxygen pressure was correlated to the body mass index.Conclusions: Sleep architecture changes are closely related to the degree of OSAHS.The daytime lung functions,blood gas analysis are not directly related to the degree of OSAHS.