We apply the method of principal component analysis to a sample of simple stellar population to select some age sensitive spectral indices .
Besides the well-known age sensitive index , H \beta , we find some other spectral indices have great potential to determine the age of stellar population , such as G4300 , Fe4383 , C _ { 2 } 4668 , and Mg b .
In addition , we find these spectral indices sensitivity to age depends on the metallicity of SSP , H \beta and G4300 are more suited to determine the age of low metallicity stellar population , C _ { 2 } 4668 and Mg b are more suited to the high metallicity stellar population .
The results suggest that principal component analysis method provides a more objective and informative alternative to diagnostics by individual spectral lines .