Abstract: The South America plate lies among the Caribbean Sea,Peru-Chile sea gouge,Nazca,COCO plate and Atlantic,which subjects to the eastward violent push of Nazca and extrusion of seafloor spreading at mid-Atlantic ridge,especially the second highest mountain Andes,where the tectonic plate activities,such as earthquakes,volcanic eruption,mountain building and other events,take place frequently,so the inter-plate deformation and plate motion are very complicated.Now it provides a guarantee for studying plate motion at an mm/a level with the rapid development of the space geodetic techniques,such as very long baseline interferometry(VLBI),satellite laser range(SLR),global positioning system(GPS) and doppler orbit determination and Radio positioning Integrated by satellite(DORIS) in twenty years.In this paper,by analyzing the plate motion,active deformation of the South America plate,and relative deformation of the Nazca-South America plate through space geodetic measurements,the South America plate is moving northward at average 14.0mm/a,shrinking west eastward at 10.9 mm/a and wholly moving eastward at 3.8 mm/a,so the mid-Atlantic ridge is moving eastward slightly while spreading,which is perhaps the reason that causes mid-Atlantic ridge at about 0~10°S to distort eastward.And this paper further analyzes the present-day plate motion and active deformation of the South America plate based on the Euler vector of the South America plate determined from an about 20-year time span of space geodetic data,incorporating the space geodetic velocity field that was free of any additional tectonic plate model assumption,so the Euler vector of the South America plate derived from space geodetic data can better describe contemporary features of the South America plate motion than the geological model NNR-NUVEL1A that was determined based on the geological and geophysical data in several million years.But the differences of deformation in the South America plate based on these two models are very significant for contemporary crustal deformation measurement in mm/a accuracy,which shows present-day motion characteristic of the South America plate.