Abstract Based on the unbiased homogeneous CIV absorption line sample constructed in paper(I), we have carried out a statistical test and analysis. The results show that there is an apparent excess of associated absorption systems (defined as those with z abs≲ z em , as Weymann et al. reported. This excess of associated CIV systems exists both in radio-loud and radio-quiet QSOs. But the excess seems to be dependent on the redshift. This is most likely a result of evolution of the interaction of QSOs, especially radio-loud QSOs, with their environment. Larger samples of high-redshift, radio-loud QSOs are necessary to confirm our result.