In the present paper, we analysed the effects of spectral resolutions and signal-to-noise ratios (SNRs) on 19 atomic absorption line indices of Lick index system. First of all, adopting method of convolving a spectrum with a Gaussian profile, we transformed spectra into those under different resolutions and then measured the line indices on them. Comparisons of the indices under various resolutions allow to investigate the impact of spectral resolution change on the accuracy of measurements of indices. Secondly, by adding random noises with different Gaussian distribution to a spectrum, the authors transformed theoretical spectra with no noises into those under diverse SNRs and then measured line indices on them. Comparisons of the indices under different SNRs greatly helped analyse the influence of SNR on the precision of the measurements of line indices. It comes from comparisons and analysis that the spectral resolution change can cause an index measurement change depending on the extent of the change of spectral resolution. Such a kind of change relationship varies with the indices. The lower the SNR, the less precise the measurements of indices. The effect of SNR on the measurements of indices can be ignored if SNR is larger than 25.