After the thin wall sampler was used in soft soil widely in the 1980 s, according to the data of the relations between soil’s stress and strain with the soil’s structure strength, the soft soil behaves quasi-elasticity before breakage and elastic-plasticity after. Many soil test data show that the soft soil’s compression and strength indexes are lineal and phased. This paper corrects the early relevant understanding about the traditional soil mechanics theory because of the ordinary sampler and technology.