提出溶液结晶第3亚稳区的概念,并对NaNO_3、KClO_3、K_2Cr_2O_7及H_3BO_3水溶液的第3亚稳区宽度进行测定,发现第3亚稳区宽度比第1及第2亚稳区要宽得多,是更为接近均相成核时的亚稳区.将描述均相成核的经典成核理论应用于第3亚稳区的计算,得到了用其它方法很难得到的固液界面张力σ、临界核半径r及临界核所含溶质分子数i. The concept of the third metastable zone in solution crystallization was proposed and the third metastable zone width of NaNO_3, KClO_3, K_2Cr_2O_7 and H_3BO_3 aqueous solutions was determined. It was found that the width of the third metastable zone is wider than that of the first and second metastable zones Is closer to the metastable zone in homogeneous nucleation.The classical nucleation theory describing homogenous nucleation is applied to the calculation of the third metastable zone and the solid-liquid interfacial tension that is hard to obtain by other methods σ, the critical core radius r and the number of solute molecules contained in the critical core i.