Abstract We construct viscoelastic deformation models and combine them with previous research results to investigate the post-seismic viscoelastic relaxation effect of six M≥7 earthquakes that occurred near the east Kunlun fault in the past century. We analyze the influence of this effect on regional crustal deformation. The results show that: 1) The crustal deformation caused by post-seismic viscoelastic relaxation of the recent 1997 Manyi M7.5 and 2001 Kunlun M8.1 earthquakes is of great significance. It can cause a crustal deformation of up to 7.6 mm/a in 10－20 a(2010－2020) after the two earthquakes, leading a cross-fault deformation rate of 8.4 mm/a. 2) The post-seismic viscoelastic relaxation of the 2021 Madoi MS7.4 earthquake is estimated to cause a maximum crustal deformation of 3.9 mm/a in the next 10 a(2021－2030), and the cross-fault deformation rate can reach 2.6 mm/a in 2025－2030. These results suggest that the effect of post-seismic viscoelastic relaxation cannot be ignored when studying the long-term crustal deformation and associated inter-seismic fault slip rate. 3) By considering the post-seismic viscoelastic deformation, the slip rate of the middle east Kunlun fault inferred from GPS velocity profile agrees well with the geological results; otherwise, the inferred slip rate will be clearly overestimated by 30%.