We focus on the accuracy analysis and improvement of multi-GNSS precise point positioning (PPP) during ionospheric scintillation. By using the observation data from Hong Kong Satellite Positioning Reference Station Network (SatRef) on 18 and 19, October 2015, the performance of kinematic PPP under the ionospheric scintillation condition is analyzed. The first day corresponds to the day of year 291, which is under the non-scintillation condition (S4 < 0.2) while the second day corresponds to the day of year 292, which is under the scintillation condition (S4 > 1.0). The results show that the GPS-only kinematic PPP solution is seriously influenced when scintillation occurs while the GPS/BDS/GLONASS combined solution can present a robust solution. Statistics results show that the root-mean-square (RMS) values of the single GPS and GPS/BDS/GLONASS combined kinematic PPP solution for the day of October 18 are stable and comparable, which are better than 5cm. However, the RMS of positioning results in single GPS kinematic PPP solution for October 19 is 0.273m, which is much worse than that of October 18. When using GPS/BDS/GLONASS combined solution, the positioning accuracy is 0.051 m, with an improvement of 81.3% compared to the result of the GPS-only solution. This indicates that multi-GNSS is an efficient way to overcome the impact of ionospheric scintillation on positioning result.