Phonon scattering has a non-negligible influence on the characteristics of carbon nanotube field effect transistor (CNTFET). Using the ballistic transport model, the device parameters under phonon scattering are analyzed, and then the CNTFET phonon scattering model is established. To reduce the complexity of this model so that simulation speed can be improved, the effects of phonon scattering is studied through analyzing chirality, temperature and energy, and therefore a new CNTFET phonon scattering model is established with linear approximation. By analyzing the scattering current changes, correctness and validity of the model are demonstrated. The proposed model is easier for calculation and has less computational complexity compared with semi-classical scattering model.