To improve the on-line monitoring rate of pig ear skin surface temperature and realize the long-term monitoring of pig ear skin surface temperature, a fast detection method based on optimal step for pig head was proposed. Firstly, five dynamic detection lines were designed to scan at the entrance of the channel. Secondly, as soon as the pig entered the channel, the optimal vertical step size was calculated by using the high temperature threshold and two vertical dynamic detection lines, so as to determine the position of the frame on the left and right sides of the pig head box. Finally, the results of the comparison between the high temperature threshold value and the temperature of the dynamic scan line in the vertical interval were used to calculate the optimal vertical movement step, and then the positions of the upper and lower edge lines of the pig head detection box were determined respectively, so as to realize the fast detection of the head based on the optimal step. The video data of 40 pigs were collected and tested on Matlab and C# platforms. The results showed that the average frame rate of the proposed method was 74.4% and 54.1% higher than that of the skeleton scanning strategy and the compressed sensing method, respectively. Compared with compressed sensing and kernel correlation filtering, the detection accuracy was improved by 11.03 percentage points and 13.82 percentage points, respectively. The mean error of ear base skin surface temperature was 0.235℃. The research result can provide technical support for the integration of the automatic detection system of pig body surface temperature.