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 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 system BER with X-ray flare 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?10^6 cm^-3；The interval-weighted channel capacity attenuation is 0.142 bit/s when the photonic quantum signal passes through the ionosphere with a thickness of 10 km and the X-ray flare radiative flux increases from 10^-5 W/m^2 to 10^-4 W/m^2; When the X-ray flare radiation intensity increases from 10^-5.5 W/m^2 to 10^-4.25 W/m^2, the weighted channel survivor function decays from 0.986 to 0.799, and the ability of the channel to maintain an efficient service state decreases significantly; When weighting the channel fidelity F=0.92, the channel establishment rate decays from 18 pairs per second to 7 pairs per second as the X-ray radiation flux increases from 10^-5.2 W/m^2 to 10^-4.4 W/m^2 , when the signal transmission distance is 6 km; When the transmission distance is 25 km and the X-ray flare 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.