Objective To explore the correlation of pulse transit time (PTT)-based beat-by-beat blood pressure monitoring with obstructive sleep apnea (OSA). Methods A retrospective analysis was conducted on 57 suspected OSA patients admitted in the Sleep Respiratory Monitoring Center, Department of Respiratory and Critical Care Medicine of the First Medical Center of Chinese PLA General Hospital from June 2021 to January 2022. Their sleep monitoring parameters and blood pressure changes based on PTT were collected and analyzed. The clinical data, respiratory event index (REI), oxygen desaturation index (ODI), time proportion of blood oxygen saturation below 90% (T90%), blood pressure increase index, and systolic and diastolic blood pressure in different postures were recorded and collected. According to the severity of OSA, age and gender, the patients were respectively divided into a mild OSA group (18 cases) and a moderate to severe OSA group (24 cases), a <60-year-old group (28 cases) and a ≥60-year-old group (14 cases), and a male group (31 cases) and a female group (11 cases). SPSS statistics 26.0 was used for data analysis. Independent-samples t-test was employed for intergroup comparison. Pearson correlation analysis was applied to analyze the correlation of REI, ODI, T90% and blood pressure increase index. Results Finally, 50 patients were enrolled in the study, and 42 of them [a mean age of (53.60±11.93) years] were confirmed with OSA. In the OSA patients, REI, ODI and T90% were moderately positively correlated with blood pressure increase index (r=0.651,0.633,0.714, P<0.001), while the lowest SpO₂ value was negatively correlated with the blood pressure increase index (r=-0.582; P<0.001). The increments of average and maximum blood pressure were weakly negatively correlated with age (r=-0.353, -0.332; P<0.05). Significant differences were observed between the patients with mild OSA and those with moderate to severe OSA in blood pressure increase index, number of blood pressure increase, average systolic blood pressure, maximum systolic blood pressure, supine systolic blood pressure, and supine diastolic blood pressure (all P<0.05). And statistical differences were also seen in average and maximum increments in blood pressure between the OSA patients aged ≥60 years and those <60 years [(13.64±0.84) vs (15.11±1.64) mmHg(1 mmHg=0.133 kPa), (23.71±6.58) vs (25.36±17.85) mmHg, P<0.05]. The male OSA patients had statistically higher blood pressure increase index, and average and maximum increments in blood pressure than the female ones [(21.75±19.96) vs (7.02±3.87) times/h, (14.97±1.62) vs (13.64±0.92) mmHg, (34.58±17.10) vs (22.73±7.23) mmHg, P<0.05]. Conclusion Beat-by-beat blood pressure measurement based on PTT technology could reflect the elevated nocturnal blood pressure of OSA patients. The severity of OSA was closely associated with increment of nocturnal blood pressure, especially in those aged <60 years and the male OSA patients.