Background: Telemonitoring has been found to improve the adherence of short-term positive airway pressure (PAP) adherence in random controlled trials (RCT) among patients with obstructive sleep apnea (OSA), however, the RCT results may not fully reflect the real-world situation of PAP management. The objective of this study was to assess the effect of web-based telemonitoring on PAP adherence in patients with moderate to severe OSA on real-world evidence. Materials and Methods: PAP therapy data for patients with OSA were retrospectively examined and were divided into two groups according to the PAP machines with or without web-based telemonitoring application (TC group or SC group). The adherence data was analyzed at 1 month, 3 months, 6 months, and 12 months after initiation of PAP therapy. Results: A total of 126 patients, including 64 subjects in the TC group and 62 subjects in the SC group, were included for analysis. Compared with those in the SC group, the percent of nights ≥4 hours of PAP use and the mean nightly duration of PAP use were greater in the TC group in the initial 6 months. However, these adherence data were comparable at the end of 12 months. The decreased rate of adherence parameters was greater in the TC group during the 3–6 months compared with the initial 1–3 months. The uptake of telemonitoring function was found to be only associated with good PAP adherence at the initial 3-month therapy. Conclusions: PAP adherence is significantly improved through telemonitoring in the first 3–6 months after PAP initiation. However, the 12-month adherence was comparable between TC and SC groups. The timing and form of interventions based on telemonitoring data that could be most effectively implemented by healthcare providers, warrants further investigation.