Indoor overheating in high window-wall ratio (WWR) buildings has drawn widespread attention, but there is limited research on it during winter. Similarly, the application of radiative cooling (RC) technology on high-WWR facades and the effectiveness of combining RC with phase change materials (PCMs) need exploration. In Guangzhou, typical rooms in commercial buildings were studied, revealing that high-WWR buildings experience greater indoor overheating in winter compared to summer. For a 100% WWR, the total equivalent energy consumption (EEC) is 71.389 in winters, 7.8% higher than summer. Using RC glass with high solar (diffuse) reflectivity (0.65) on south-facing windows reduced EEC by over 70%. RC glass also provided significant cooling capacity during unoccupied periods, which is sufficient to meet daytime cooling needs. In the case of a 100% WWR, the proportion of available cooling capacity (37.5%) during unoccupied period exceeded daytime cooling EEC (24.9%). Therefore, PCMs were adopted to store this cooling capacity and transfer it for release during the occupied period, which bring an additional improvement in energy-saving performance by 4.7%. The combination of PCMs and RC technology further achieves building energy efficiency. This study offers insights for addressing winter indoor overheating in high-WWR buildings.