Solid lung nodule is the imaging representation of solid lesion ≤3cm in the lung, which can be seen in lung tumor, tuberculosis, necrotizing granuloma and so on. 1. Lung tumor: primary lung cancer is often a single nodule, with visible burrs at the edge, which can be connected with the pleura; lung metastases are often multiple, with different sizes and clear edges. 2. Tuberculosis: it can be a round tuberculosis ball with proliferative or fibrous foci scattered around it, called satellite foci; it can also be millet-type tuberculosis, mostly <3mm millet-like nodule shadow, with the characteristics of uniform size, distribution and density. 3. Necrotizing granuloma: it is an inflammatory and proliferative lesion in the lungs, and the nodules can be adenoidal-sized nodules (diameter ≤1cm) with clear margins. If you find solid nodules in the lungs, you should go to a regular hospital in time to get a clear diagnosis and active treatment.