Abstract: Abstract: In order to build a path loss model and optimize the deployment of ZigBee nodes, in this study, how the characteristic affecting the wireless signal propagation in pig farm environment is evaluated. The research is based on ZigBee wireless sensor network technology. Depend on the environment of pig farm, we consider piggery wall and plant growing between piggeries as the two mainly barriers which affect the wireless signal propagation greatly. During the research, packet loss rate (PLR) of wireless signal and received signal strength indicator (RSSI) are the most important parameters being used to evaluate transmission characteristics. We chose direct ray model as the basic path loss model and designed three groups of experiment to measure the parameters used in the model. Firstly, we tested RSSI value changed with the distance between transmitter and receiver in the case of no obstacle for 12 times. Based on the data obtained by regression analysis, the path loss exponent value was 2.02 and the correlation coefficient was higher than 0.9. Secondly, the influence of barrier was taken in count. The thickness of piggery wall was 0.4 m and the antenna height was set at 1.2 m for avoiding the effect of other obstacles. By increasing the number of wall, the rate of packet loss obviously changed. Result showed that one or two walls have no influence on PLR value, but it turns to 17.75% when the number of walls increases to 3 and when the number of walls added to 5, with PLR value reaches 100%. The influence of wall is transformed into the wall attenuation factor that added into the path loss model, and its value is computed to be 2.64. There are plants growing between the piggeries, which can be divided into three groups, 40, 80 and 120 cm. We set 4 groups of antenna heights for each kind of plant, which is depending on their own height. At each antenna height, we tested RSSI value with the changes of distance between transmitter and receiver, and then get the varying pattern of plant attenuation factor with the antenna height based on the regression analysis. Results showed that plant attenuation factor decreased with the rising of the height of installing antenna. Finally, prediction path loss model with the wall attenuation factor 2.64 and the plant attenuation factor, we use multi stage function to express when the plant height is 40, 80 and 120 cm, were obtained. In order to test the accuracy and practicability of the model, the integrated experiments with both wall and plant as the barriers in the pig farm environment were investigated, and the model was verified according to the field-test result. In the model, the path loss exponent is 2.02 and the basic path loss value is 63.602 dBm and other parameters change with the plant height or antenna height. The model is a comprehensive model that can be used for predicting the path loss value of ZigBee wireless signal in the pig farm environment. On the basic of the prediction path loss model, we can optimize the node deployment for increasing the network coverage rate and connectivity.