In response to the demand for improving the performance of large-size 5B70 forged rings， through thermal compression simulations of the 5B70 homogenized at different temperatures and strain rates， stress and strain data were obtatined and the hot-working diagram of the alloy was fitted to guide large-size forged rings formed. The suitable processing temperature of the alloy is 400 ℃ to 450 ℃， and the most suitable deformation rate is 0.1/s. According to hot-working diagram ， the ring forging process with the same conditions was used to prepare 5B70 alloy test pieces and finished ring piece with the size of Ф2 900 mm×Ф2 600 mm×700 mm， and the microstructure and properties of the ring were studied. The results show that the 5B70 Al-Mg-Sc alloy can obtain good mechanical properties and performance of plastic deformation under the theoretical thermal deformation conditions.