The GPS 1 Hz and 30 s sampling observation data published by UNVAVCO were processed and analyzed with the double difference position method, then the dynamic ground deformation and coseismic three-dimensional deformation field during the Alaska M_W 7.8 earthquake on July 22, 2020 were obtained. The results showed that the seismic waveform of high-rate GPS within 270 km of epicenter is obvious, and the maximum amplitude is 600 mm. The amplitude and response time of dynamic deformation waveform of each GPS station are greatly affected by the rupture propagation direction of earthquake and site effect. The static coseismic displacement vector points to the epicenter, and the coseismic displacement basically decreases with the increase of epicenter distance. Except for station AC13, the maximum horizontal displacement of the station nearest to the epicenter is 26.7 cm.