Quasar outflows are important for understanding the co-evolution of supermassive black holes (SMBHs) and their host galaxies, since the outflow probably regulates the star-formation activity in the host galaxy (the AGN feedback). The velocity profile of high-ionization broad emission lines such as CIV1549 in quasar spectra often shows a significant blueward asymmetry, suggesting the presence of a powerful outflow in broad-line regions (BLRs). It has been reported that the outflow strength and metallicity in BLRs of quasars show a positive correlation, that gives us important insights on the nature of the outflow (Wang et al. 2012). However, other parameters than the metallicity may also affect the quasar outflow, such as the Eddington ratio. In this study, we analyze the rest-frame UV spectra of BOSS quasars and investigate the relation among the outflow, metallicity, and the Eddington ratio. We report the results of the statistical analysis in this poster contribution.