The isothermal compression of TA 15 alloy has been carried out at a Thermecmaster-Z simulator. The experimental results show that the peak stress and steady stress decrease greatly with increasing of deformation temperature and decreasing of strain rate, and that the deformation temperature will affect the threshold strain to transmit the steady deformation. According to the experimental results, the obtained processing map presents two unsteady zones of high temperature deformation of TA 15 alloy, including the zone above 1300 K of deformation temperature and 10.0 s^-1 of strain rate and another zone below 1200 K of deformation temperature and 0.006 s^-1- 1.995 s^-1 of strain rates. Meanwhile, the present constitutive equation represents the effect of deformation temperature, strain rate and strain on flow stress in high temperature deformation of TA15 alloy. The calculated results of flow stress are in good agreement with the experimental results in high temperature deformation of TA 15 alloy.