X-ray imaging has wide application in the areas of health-care, non-destructive detection, and so forth. When X-rays penetrate through human tissues or workpieces of different density and thickness, varying degrees of the radiation are absorbed. We can detect and diagnose diseases which are not visible to the naked eye, or detect the properties, size and distribution of various macroscopic or microscopic defects inside objects through the variation and distribution of the X-ray intensity. In recent years, the design of X-ray imaging equipment with higher resolution, lower dosage and lower cost has been the goal of manufacturing companies and scientists in this field. This paper reviews the development of X-ray detectors from the perspective of their structure and materials, and discusses the absorption and performance characteristics of different detection materials. Finally, we survey the future development of X-ray detectors.