To observe the effect of continuous positive airway pressure (CPAP) on cognitive function and its relationship with growth hormone (GH) and insulin growth factor-1 (IGF-1) in patients with moderate to severe obstructive sleep apnea syndrome (OSAS). Methods: Total 39 patients with moderate or severe OSAHS were assigned to the OSAHS group and further divided them based on treatment type to into the CPAP treatment (20 cases) and conservative treatment (19 cases) subgroups. During the same period, 20 healthy physical examinees were recruited to control group. The treatment duration was 3 months. Polysomnography (PSG) data, cognitive function, and GH/IGF-1 level of all subjects were assessed before and after treatment. Results: Compared to the control group, the OSAHS group showed increased AHI, TS90%, and (N1+N2)%; decreased LSaO2, N3%, REM%, and sleep latency; and decreased MOCA total score, visuospatial and executive function, attention, delayed recall score, and IGF-1 and GH levels (all P<0.05). Pearson correlation analysis showed that, for the OSAHA group, MOCA score was negatively correlated with ESS score, AHI, (N1+N2)%, and TS90% and positively correlated with LSaO2, N3, REM ratio, and IGF-1 levels. After 3 months of treatment, the CPAP subgroup showed decreased AHI, TS90% , and (N1 + N2)% and increased LSaO2, N3% , REM% , MOCA total score, visuospatial and executive function, attention, delayed recall score, and IGF-1 and GH levels compared to before treatment and to the conservative treatment subgroup after treatment (all P<0.05). Conclusion: CPAP treatment can improve the sleep respiratory parameters and cognitive function of patients with moderate and severe OSAHS and increase the levels of GH and IGF-1.