This paper investigates the effect of 06-09-2017 X9.3 solar flare on Global Navigation Satellite System(GNSS)signal and positioning performance.To conduct the study we select 60 IGS stations and collect the observations and ephemeris from August 30 to September 13,2017.The Solar activity Indexes of Ap,Kp,Dst are evaluated and the global ROTI maps are constructed to indicate and define the magnitude of the storm.As for the GNSS signal,signal-in-space-ranging-errors(SISRE)is used to assess the solar flares effect on the accuracy of broadcast ephemeris,and the cycle slip occurrence is used to assess its impact on observation quality,especially phase observation.Furthermore,the kinematic GNSS PPP solution is used to evaluate the GNSS positioning performance during the storm.After processing,root mean square errors(RMS)of north,east and up component were calculated for each station on each day.The results indicate that at eight of all the selected IGS stations three-dimensional(3D)accuracy of PPP has degraded significantly and the GNSS are unreliable during the storm.