Based on CT alone, it is sometimes difficult to tell whether the lung cancer has developed brain metastasis. In this case, we can combine with enhanced CT and cranial MRI. Plain CT, as a primary screening test, is more sensitive to hemorrhage and is not precise in detecting tiny brain tumors, but its accuracy is lower than that of intensified CT and MRI. Enhanced CT can generally detect brain metastases. On enhanced CT brain metastases generally show irregular thick-walled enhancement or ring-like enhancement with nodules, as well as regular, uniform thin-walled enhancement. Cranial enhancement magnetic resonance, as a standard examination method for diagnosing brain metastases, can detect scattered and smaller tumors that cannot be detected by CT, and more brain metastatic lesions can be detected by using double contrast and thin-layer scanning when necessary. Patients are advised to choose the suitable examination method under the guidance of doctors to make a clear diagnosis as early as possible.