Methane is an important energy source for modern industrial production and social life, and its effective detection and segmentation are important for the timely detection of methane leaks and identification of its diffusion range. To address image problems such as blurred contours of methane gas, low contrast between leaking methane gas and the background, and susceptibility of the shape to atmospheric flow factors under infrared imaging conditions, this study proposes an infrared image segmentation network (attention branch feature network (ABFNet)) incorporating attention branch features to achieve methane gas leak detection. First, to enhance the feature extraction capability of the model for IR methane gas images, a branch feature fusion module was designed to fuse the output features of residual modules 1 and 2 with residual module 3 in a pixel-by-pixel summing method to obtain rich and detailed feature expressions of IR methane gas images to improve the model’s recognition accuracy. Second, to further accelerate the inference speed of the model, the 3×3 convolution in the standard bottleneck unit was replaced with a depth-separable convolution to significantly reduce the number of parameters required for real-time methane gas leak detection. Finally, scSE attention mechanisms were embedded in the branching feature fusion module to focus more on the edge and center semantic information of the diffusion region to overcome the problem of low contrast of the blurred IR methane gas contours and improve the generalization ability of the model. The experimental results showed that the quantitative segmentation accuracy of the proposed ABFNet models AP50@95, AP50, and AP60 reached 38.23%, 89.63%, and 75.33%, respectively, with improvements of 4.66%, 3.76%, and 7.04%, respectively, compared with the segmentation accuracy of the original YOLACT model. The inference speed reached 34.99 frames/s and met the demand of real-time detection. The experimental results verified the effectiveness and engineering practicality of the proposed algorithm for infrared methane leak detection.