Modern classification: in order to adapt to the development of modern poultry industry, it can be divided into egg line and meat line (ie, laying hen line and broiler line) according to economic performance. (1) Egg laying line: used to produce commercial eggs. According to the different colors of eggshells, they can be divided into white-shell laying hens and brown-shell laying hens. Its characteristics are: generally smaller, longer, developed hindquarters, thin skin and bones, strong muscles, tight feathers and lively temperament. Generally, they can lay 270-300 eggs a year. (2) Broiler line: Broilers are mainly bred by crossbreeding. It is characterized by its large size, wide, deep and short body, muscular chest and square cylindrical appearance. Small crown, short and thick neck and thick talus; Muscular, gentle, slow-moving, fast-growing, easy to fatten, generally raising for 6-7 weeks can reach more than 2 kg. (II) Introduction of Foreign Laying Hens Introduced in China The main laying hens introduced in China are: (1) Roman Brown: a medium-sized high-yield laying hen selected by Roman Company in Germany, with four-line matching and feather color linkage genes. (2) Issa Brown: bred by Issa Company of France, it belongs to four-line medium-heavy and high-yield brown shell laying hens. With good heat resistance, it is one of the main high-yield laying hens in the world at present, with two sex-linked genes: feather color and fast and slow feather. (3) Rose Brown: It is a high-yield laying hen bred by British Ross Company, with strong adaptability and good stress resistance. There are two sex-linked genes: gold and silver and fast and slow feathers. (4) Dika Warren (brown): It is an excellent brown-shell laying hen bred by Dika Poultry Breeding Company of the United States. Four-line matching, with feather sex gene, can be divided into male and female. (5) Xingza 579 (Brown): also known as S579, bred by Schaefer Company of Canada. Chickens have the sex inheritance of feather color, and they can be distinguished according to the different feather colors. (6) Hesse (brown): a medium-sized brown shell laying hen cultivated by Cheng Yulibud Company in the Netherlands. Genes with feather color and sex. This kind of chicken is gentle in temperament, easy to manage, strong in cold resistance and stress resistance, and has the characteristics of long laying peak period and few broken eggs. However, the heat resistance is poor, so it is suitable for breeding in cold areas in the north. (7) Hyland Brown: Medium-sized brown shell laying hens cultivated by Hyland International Company of the United States. The chicken has docile temperament, good adaptability, early laying, early laying peak and long duration, and has feather color linkage genes. (8) Xingza 288 (white): also known as s 288, bred by Schaefer Company of Canada. The body shape and coat color are similar to those of white leghorn chicken, but the weight is lighter. This kind of chicken has the characteristics of less feed consumption, more eggs, heavy eggs and no nesting.