The tensile stress-strain curves and creep curves of commercial pure titanium TA2 at service temperature range (room temperature, 353K, 423K) were observed by tensile testing and creep testing. Based on the creep testing results, the significant creep phenomenon was observed at the service temperature range, and the creep feature was changing with temperature. Then, the tensile constitutive equation and the creep constitutive equation were constructed for TA2. Combining the tensile and the creep constitutive equations, the isochronous stress-strain curves were generated. The isochronous stress-strain curves of TA2 were much lower than the tensile stress-strain curves, and the isochronous stress-strain curves are decreasing with design life. Moreover, the variation feature of isochronous stress-strain curves with design life is changing with temperature. Based on the isochronous stress-strain curves, allowable limit strain and design life, the time dependent allowable stress of CP-Ti was proposed.