In order to solve the problem of pig temperature automatic extraction by infrared thermography, based on the infrared inspection device of pig body temperature in facility farm, an automatic pig ear temperature extraction algorithm IT-PETE, based on infrared thermography, was proposed to identify the ear region of pigs efficiently and accurately and extract the maximum and average values of the ear region to achieve noncontact automatic monitoring of pig body temperature. Specifically, Laplace operator was used to preprocess the thermal infrared image of pigs, then extract the ear of pigs from the thermal infrared image based on YOLO v4 and morphology, and automatically the maximum and average temperature of the ear region was obtained by combining the ear segmentation image and the temperature matrix. The detection model of pig ear region was trained by five fold cross validations, with 2000 infrared thermal images as training and validation sets, and 400 images as test sets. The YOLO v4 detection accuracy of ear region reached 97.6%, which was 2.0 percentage points and 7.8 percentage points higher than that of Faster R-CNN and SSD, respectively. The average detection time of single frame image was 12ms. Meanwhile, through the analysis on the correlation between the artificial statistics of the ear temperature data of 20 pigs and the body temperature extracted by the algorithm, it was obtained that the correlation between their maximum and average temperature in the ear area was 0.9849 and 0.9119 respectively, which showed the reliability and application of the IT-PETE algorithm to extract the body temperature data. Therefore, IT-PETE algorithm can provide technical support for automatic monitoring and early warning system of pig body temperature to a certain extent, with a good application prospect.