It is a challenging task to separate infrared (IR) small targets from complex backgrounds quickly and accurately. Many kinds of literature have designed various feature fusion modules to further extract IR small target features. Although these designs are slightly helpful to the improvement of IR small target detection accuracy, they will cause a significant increase in network params and FLOPs. To minimize the computational complexity of the network and achieve industrial implementation while ensuring accuracy, we abandon the complex feature fusion modules and combine regular convolutions, depthwise separable convolutions, atrous convolutions, and asymmetric convolutions modules to form a new lightweight encoding and decoding structure, which called lightweight IR small target segmentation network (LW-IRSTNet). In addition, we design the post-processing modules, which include an eight-neighborhood clustering algorithm and an online target feature adjustment strategy. The experimental results show that: 1. The segmentation accuracy metrics of LW-IRSTNet are the same as the best results of 14 state-of-the-art comparative baselines; 2. The params and FLOPs of LW-IRSTNet are only 0.16M and 303M, which is much smaller than the comparison baselines; 3. The post-processing module increases human-machine friendliness and improves the robustness of the algorithm in application deployment. Meanwhile, LW IRSTNet is deployed on both embedded platforms and the website, further expanding its application scope. Through the ONNX framework, NPU acceleration, and CPU multi-threaded resource utilization, the high-performance inference capability and online dynamic threshold adjustment ability of LW-IRSTNet are realized. The source codes are available at https://github.com/kourenke/LW-IRSTNet.