The ionosphere is an important component of the solar-terrestrial space environment, and the delay error is the mainly error source in Global Navigation Satellite System (GNSS). For GNSS single-frequency users, broadcast ionospheric models (BIMs) play an important role in mitigating the ionospheric delay. Solar activity induces ionospheric disturbances, which can reduce the performance of the GNSS. In this study, the influence of solar activities on GNSS BIMs was analyzed in the Asia-Pacific region. Twelve X-class and M-class large solar flares were selected for this study. Total electron content (TEC) derived from selected International GNSS Service (IGS) and Crustal Movement Observation Network of China (CMONOC) were used to analyze the variation of the TEC anomalies and the adaptability of the GNSS BIMs during sample solar flare events. It is verified that very noticeable Sudden Increase in Total Electron Content (SITEC) clearly took place during solar flares. The temporal variation of rate of TEC (ROT) is more pronounced and rapid with respect to that of TEC. Especially, the influence of solar flare on the correction accuracy of GNSS BIMs is significant, as illustrated by a noticeable decrease in relative difference (RD) between the observed and modeled TEC values of the GNSS BIMs occurred during the events. Through our investigation, we found that the adaptability of BDS BIM is better than GPS and Galileo BIMs under solar flare conditions because its coefficients were updated more frequently, while the accuracy of the Galileo BIM is the highest among the GNSS BIMs.