T-SPICE model of GaAs HEMT

There isn't any such T-SPICE model for HEMTs. Instead, there are some standard models such as TOM, Angelov,Skallern-Parker,Statz etc. and these models are-generally- recognized by professional SPICE ( or SPICE-like) simulators.All you should do is to find a proper model for your transistor and implement into your netlist this transistor by using this convenient model.
in order to get which models are recognized by Tanner tool, refer to help and model help..( some models may not be recognized, take care..)

Can you please suggest me, exactly how to create HEMT model in tanner tool. Because HEMTs diagram consist of physical layers and i am not getting its exact equivalent circuit diagram. So, can you help me regarding this.

You would extract a HEMT model from a physical layout view ? I couldn't understand your question.