We have considered the mass loss effects on the analytical PMS stellar evolutionary model of Stein(1966). In this calculation, we have assumed the mass loss law, M˙=K(L/C)(R/GM)'-,which should be reasonable for PMS stellar wind mechanism. The numerically obtained evolutionary tracks in H-R diagram indicate that the higher mass losses PMS star have, the later they reach the radiative equilibrium. We have considered the composition effect on the evolution such as the composition difference between Pop. I and Pop. II PMS stars. We have also compared the tracks under the mass loss law, M˙=K'LR/GM.

Under the context of Stein's linear theory of stellar models, the luminosity-effective temperature relationship is derived for contracting pre-main sequence stars which are losing mass, according to the empirical formula, given by Reimers (1975). The effects of mass loss on their evolution are investigated by calculating evolutionary tracks of 1. 1.5M⊙ 1.5M⊙ , 5M⊙ 5M⊙ , and 10M⊙ 10M⊙ , stars. Our calculations reveal that the effects of mass loss show up in the radiative equilibrium stage of the evolution. It is found that an increase of mass loss rate leads to delay the onset of radiative equilibrium, thus resulting in under-luminous main sequence stars. It is also noted that the mass loss prolongs the pre-main sequence life time. Detailed results of the calculations are discussed.