| Studies on the chemical abundance in galaxies are very important to understand the physicalprocesses in galaxy formation and evolution, and provide strong constraints on its framework. Inliteratures, two main aspects are often studied: one is to understand how metallicity evolves withtime, and the other is try to find the relationships between metallicity and macroscopic propertiesof galaxies. Both of them are keys to understand galaxy evolution process, the former re?ectingthe gas reprocessed by stars and any exchange of gas between galaxy and its environment, andthe latter giving us more clues about star formation, gas out?ow and other physical processesthat govern the galaxy formation. In this article, we focus on the latter, i.e., analyze the mass-metallicity relation of galaxies in detail.It is of particular interest to study the evaporation of metals from galaxies into the intra-clustermedium (ICM) and/or inter-galactic medium (IGM) which has been observationally confirmed.Based on the galaxy formation and mass out?ow models suggested by Mo et al. (1998) and Shuet al. (2005), the correlation between the galactic wind velocities and the escaping velocities ofpotential wells of galactic dark matter halos is discussed. It is found there is a critical value of therotation velocities of galaxies (～100-150 kms-1), below which the mass outflows really escapefrom their host gravitational potentials, otherwise the mass out?ow falls back to the galaxies toform galactic fountains. Taking this into account and assuming that small galaxies lead to strongmass loss due to galactic winds, we can reproduce the observed mass-metallicity relation for diskgalaxies fairly well.
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