Nano thinfilm transistor (TFT) is fabricated at the root of a beam, which becomes the maximum stress area when the beam is bent. In this process, a probe is used to bend the beam and produce GPa-order mechanical stress. The electrical characteristic of TFT under different GPa stress has been studied. Threshold voltage , relative drain current change , and transconductance present a nonlinear relationship with increasing GPa-order stress. Analyzed from experimental results, channel piezoresistivity effect below 1.82 GPa stress, energy valley splitting, large change of valence effective mass from 1.82 to 2.08 GPa, and interface effect above 2.08 GPa are the factors of nonlinear change of parameter with GPa-order mechanical stress.