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To address the issues of complex background in foreign object images, weak feature extraction, low detection accuracy for adhering small objects, and distortion in detection box positioning and scale, a foreign object detection algorithm for mining conveyor belts based on YOLOv5n-CND is proposed. First, the C2f module was used to optimize the feature pyramid, using fewer parameters to address the issue of poor sensitivity to small object detection caused by the complex background in foreign object images and interference from complex objects in underground environments. Second, the normalized Gaussian Wasserstein distance (NWD) regression loss function was used to replace CIoU, improving the performance of multi-scale foreign object detection and accurately predicting the detection of adhering small objects. Finally, a detection head (DyHead) was added, combining three attention mechanisms: scale, spatial, and task, to enhance feature extraction for foreign object contours and improve the adaptability to multi-scale targets. Experimental results demonstrated that YOLOv5n-CND achieved an mAP@0.5 of 87.9%, an mAP@0.5:0.95 of 55.9%, a parameter count of 4.49×106, and a detection speed of 85.5 frames per second, meeting the requirements for underground foreign object detection in coal mines. The mAP@0.5 and mAP@0.5:0.95 of YOLOv5n-CND were 2.6% and 3.4% higher than YOLOv5n, and 1.7% and 3.8% higher than YOLOv5s-CBAM, respectively. Although the model’s parameter count slightly increased compared to the YOLOv5n model, it was still lower than that of other models. Tests were conducted in four scenarios: foreign objects with elongated shapes resembling the background; anchor bolts with relatively low lighting; objects heavily mixed with coal gangue; and multiple foreign objects. The results indicated that the foreign object detection algorithm for mining conveyor belts based on YOLOv5n-CND did not result in false detections or duplicate detections, with very few missed detections. The detection box positioning was accurate, and the handling of adhering small objects was more effective, enabling precise detection of foreign objects on conveyor belts.