CO_2 is a major part of the atmosphere and is a member of greenhouse gases. It is not just a major contributor to global warming. And it is one of the harmful gases that cannot be ignored in the pigpen. In recent years, with the development of scale and intensive pig housing, the research on the factors affecting the temperature, humidity, NH3, H2S and CO_2 in the piggery is increasing. CO_2 plays an important role in the environment of piggery and is an important parameter to evaluate the environmental quality of piggery. The effective management of CO_2 in piggery can improve the management level of piggery breeding and maximize economic benefits. This article first expounds the main source of CO_2 emissions of piggery pig breath, waste discharge, heating equipment, analyzes the CO_2 emissions are mainly affected by the external environment, the number and type, volume of piggery and pig manure storage time and other factors. The CO_2 emissions of live pigs in different growth stages of weaning, breeding, fattening and sows were compared and analyzed under conditions of leaky floor, partially leaky floor, straw mat and wood chip floor. Discusses the inner generated by different concentration of CO_2 in breeding, pig physiological behavior, the influence of the pork quality, according to CIGR data, draw corral CO_2 concentration limit was 0.3%, the largest of the CO_2 concentration limit of 0.5%, In piggery CO_2 content is too high, the content of oxygen deficiency, for a long time can cause a chronic hypoxic pigs, depression, loss of appetite, weight gain, slow, weak, susceptible to infectious diseases, the problem such as production levels drop, serious when, after the death of a pig appeared ecchymosis, slaughter appear blood, flesh PH, conductivity, moisture content decreased, affect significantly the quality of pork. Secondly, the method of CO_2 content monitoring in the shed and the research progress at home and abroad are summarized. Inductive analysis of the strength of CO_2 and ventilation, ventilation rate, the relationship between the air inlet position, in detail elaborated the cesspit ventilation system by changing the intensity of ventilation, air inlet location, the size of the floor openings, can effectively reduce CO_2 in the house. Calculate the ventilation rate in piggery of there are three kinds of methods, one is to use the animals themselves to calculate temperature balance, 2 it is used to measure the air humidity, three is the CO_2 balance equation method, calculate the ventilation rate of the current mainstream approach is the use of CO_2 from the air balance characteristics, monitoring CO_2 concentration, according to the concentration of CO_2 and ventilation rate equation, the relationship between the size of the calculation of ventilation rate. Finally, according to the actual research situation, the future research direction and development trend of CO_2 content in piggery are prospected.