A thermo mechanical treatment method for providing super-plasticity to Al--Li alloy being a kind of light and high strength alloys. The thermo mechanical treatment method according the invention comprises steps of, homogenizing Al--Li alloy consisting of Al--Cu--Li--Mg--Zr at a temperature of 500.degree.-500.degree. C. for 10-30 hours, and controlled rolling the alloy at a temperature of 300.degree.-500.degree. C., a rolling speed of 2-20 m/min and a draft percentage per pass of 2-18%. The thermo mechanical treatment of the invention has a wide industrially applicable range and thus an excellent operation efficiency. The thermo mechanical treatment exhibits excellent super-plasticity at a higher strain speed as compared with known treatments.