Abstract: Both crop and livestock play key roles in agricultural system. In the integrated crop-livestock production system, there is an intact net of matter flow and energy flow between crop sub-system and livestock sub-system and residues of one sub-system often are used as raw material of another one. The interaction between crop and livestock has promoted evolution of agricultural system and there have been six stages: Originally hunting and foraging system (OHF), originally integrated crop-livestock production system (OICL), extensively specialized production system (ES) including extensively specialized crop production system (ESC) and extensively specialized livestock production system (ESLP), extensively integrated crop-livestock production system (EICL), intensively specialized production system (IS) including intensively specialized crop production system (ISC) and intensively specialized livestock production system (ISL), intensively integrated crop-livestock production system (IICL). And there have taken place two specializations and three integrations of crop production and livestock production during evolution of agricultural system and productivity has risen in a spiral. Integrated crop-livestock production system comprises six dominant types: classical system (C-ICL), system based on rangeland (ICL-R), system based on crop/forage rotation (ICL-CF), system based on sown pasture (ICL-SP), system based silvo-pasture (or woodland) (ICL-W, agro-silvopastoral system) and system based on pond (ICL-P). Furthermore, one type of system could succeed to the other one along the given environmental gradient. Intensive agricultural system is mainly prevalent in developed countries, whilst extensive one is dominant in developing countries, and intensive system is significantly different from extensive system in light of components, interaction of crop and livestock, input of outside, productivity and management goals. Crop-livestock interaction in integrated agricultural system has significantly positive effects on soil quality, crop production, microorganism activity, livestock production, nutrition circle, energy efficiency and economic profitability. In terms of property, succession, structure and function of integrated crop-livestock production system, there exit some similarities and distinctions between domestic and international research. However, the current research is in face of some common difficulties, which mainly include incompleteness of research object, singleness of research scale, unreliable methods, ignoration of livestock subsystem and gap between energy analysis and matter analysis.