This review was performed to investigate the current researches on the welfare of rearing environments system in farming chicken, including stocking density, perch, housing system and research trend. The investigation indicated that most of the developed countries took much efforts into making appropriate regulations to improve the welfare of rearing environment about broilers and laying hens, particularly more parts in laying hens. Recently the regulations have varied a lot, to be more detailed than before. Moreover, some regulations give valuable suggestions to improve well-being of poultry industry such as additional facilities. Until now it has been known, the quality of the products will improve and the income of producers will increase along with the improvement of welfare. Therefore the relevant agencies and organizations can strengthen the belief of consumers especially the competition is so fierce today. In conclusion, improvement of poultry welfare should be carried out in the real situation and international trends to create the appropriate rules such as professional consulting and training.