In order to study the impact of X-ray flares caused by solar activities on the communication performance of the quantum satellite-terrestrial link,this paper constructs an ionospheric electron density increment model based on Chapman theory,and obtains the ionospheric extra attenuation factor about the X-ray flares radiation flux and the solar zenith angle based on this model.The variations of mean-based weighted channel capacity,interval-based weighted channel survival function,quantum channel establishment rate and quantum key distribution (QKD) system bit error rate (BER) with X-ray flares radiation level are analyzed by simulation.The results show that under the interference of X-ray flares,the maximum increment of electron density in the ionosphere can be as high as 2.78×106 cm-3.The mean weighted channel capacity attenuation is 0.142 bit/s when the photonic quantum signal passes through the ionosphere with a thickness of 1 km and the X-ray flare radiative flux increases from 10-5 W/m2 to 10-4 W/m2.When the X-ray flares radiation flux increases from 10-5.5 W/m2 to 10-4.25 W/m2,the interval-weighted channel survivor function decays from 0.986 to 0.799,and the ability of the channel to maintain high efficient service state decreases significantly.When weighted channel fidelity F′=0.92,the channel establishment rate decays from 18 pairs per second to 7 pairs per second as the X-ray flares radiation flux increases from 10-5.2 W/m2 to 10-4.4 W/m2 ,when the signal transmission distance is 6 km.When the transmission distance is 15 km and the X-ray flares radiation level is heavy,the BER of the key distribution system is as high as 0.021,and the BER increases with the increase of electron density.Therefore,the impact of X-ray flares on the satellite-terrestrial quantum communication link should not be ignored,and the parameter indexes of the quantum satellite can be adjusted appropriately according to the radiation level of X-ray flares to ensure the reliability and effectiveness of the communication.