Abstract: CD( circular dichroism spectra) was applied to research on the relationship between surface hydrophobicity( SH) and secondary structure in six varieties of soy protein isolate( SPI). First step was the extraction of SPIs,the functional abilities( surface hydrophobicity and solubility) and the secondary structure of the six varieties of SPI were measured and analyzed.Through SPSS software,the numerical linear correlation bewteen surface hydrophobicity and secondary structure of six varieties of soybean protein isolate was analyzed to explore the structure- activity relationship between them. The results revearled that there were significant differences( p < 0.05) bewteen the secondary structure and the functional abilities( surface hydrophobicity and solubility).The SH of the six varieties of SPI increased with the decrease of α- helix content,and decreased with the increase of random coil and β-sheet content,and the linear relationship between the SH and β-turn content was not obvious. SPSS linear correlation analysis showed that the SH of the six varieties of SPI had no significant linear relationship with β-turn content,positively related to random coil and β-sheet content,and negative correlated to α-helix content.