The article makes a basic introduction to the halo formation theory. The mass growth of dark matter halos includes two componenets: halo-halo merger and continuous accretion.Halo-halo merger can be associated with galaxy-galaxy merger, so a proper defi-nition to it is important. However there're a lot of influencing factors preventing us from geeting a reliable fitting form.The difficulties mainly comes from definitions: the definitions of halo-halo merger, the definition of constructting a merger tree, the definition of the halo mass and even the time step. We make some comparisons between different definitions and obtain the halo merger rates corresponding to them. In addition, we find the environment of haloes can also lead to different behaviors in merger rate. There fitting to the halo-halo merger rate with simulations can be carried out two folded: fitting to different redshift or fitting to the halo mergering histories. Usurally, the latter gives a universal fitting formula to haloes with different mass.%系统介绍暗晕-暗晕并合在理论方面的形成与发展,并简要介绍了其在数值模拟检验(冷暗物质模型)及拟合方面的进展.暗晕-暗晕并合率问题可与星系-星系并合率联系,正确地定义暗晕-暗晕并合率很重要,影响并合率的因素却很多,从数值模拟所得到的拟合公式往往存在较大差异,这些差异主要来自于定义:对并合的定义(并合树的建立),对暗晕质量的定义以及并合暗晕前身质量比的定义.数值模拟输出的时间步长也会对此有所影响,此外暗晕并合率也与环境强烈相关.对这些因素所导致的差异做了简单比较.此外,对于暗晕并合率的统计可分为对不同红移处的拟合和对z=0时刻对其并合历史的拟合,其中后者对不同质量的暗晕往往能给出一个较统一的拟合公式.
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