High concentrations of particulate matter (PM) emitted from animal feeding operations (AFOs) may adversely affect the health of the farmers and welfare of animals. Large quantities of PM released to the atmosphere can be transported away from sources causing environmental problem and health issues of people living in the vicinity of farms as well. PM characterization was mainly talked about inside and outside of the mechanical ventilation of caged laying hen house which used the fan to release PM outside of the house, and the propagation law of PM was studied as well. Results showed that the concentration of fine PM, which was the most harmful to the human body, was mainly derived from the inside and outside of the house, and the concentration of the PM outside was up to 55.2%, which mainly came from inside;the smaller the PM size was, the farther the distance was away from the air, which was more likely to affect the health of the vicinity of the farms;by analyzing the concentration inside and outside of daily variation of PM, it was found that the inner staff activities and feeder disturbance inner deposition of PM led to the laying hen activity enhanced which would increase the concentration inside and outside. At the same time, indoor and outdoor PM concentrations were increased with the age of laying hen and air humidity;meanwhile, to control the indoor PM concentrations and using the appropriate measures to remove the indoor PM would help to ensure the health of staffs and welfare of animals, and reduce the hazards of PM to the surrounding environment.