Subcortical U fibers, also known as arcuate fiber, are kind of short connective fibers connecting adjacent brain gyrus. They located in the outermost layer of white matter, adjacent to the cortex. With the development of imaging, more and more attention has been paid to the differential diagnosis of subcortical U fibers in different white matter lesions. In this article, subcortical U fibers are reviewed from the aspects of definition, anatomy and physiology.