In the present paper, the conclusion we arrive through analyzing the (dTc/dλ)-λ curve is that the Tc-λ curve is composed of three parts with entirely different properties, namely, "McMillan region", "λn region" and "series solution region". This conclusion is identical with that obtained in paper 20 except that the value of n is, in general, not equal to 1.55 but is a real number larger than 0.5 and varies with, the shape of the effective phonon spectrum.