In the process of metal laser additive manufacturing, the extreme nonequilibrium solidification environment withultrahigh temperature gradients, ultrafast solidification rates and cyclic thermal loads of the melting pool can easily lead tothe generation of defects such as pores and cracks, which affect the internal quality and mechanical properties of thecomponents. Traditional material characterization methods are limited by the opacity of materials, making it difficult tocapture real-time information during metal laser additive manufacturing. In contrast, synchrotron X-ray imaging has highspatiotemporal resolution and can be used to realize in situ characterization of melting pool dynamics and defect evolutionduring metal laser additive manufacturing. This article reviews the research progress of synchrotron X-ray imaging in thefield of metal laser powder bed fusion additive manufacturing, summarizes common types of defects in additivecomponents and their characterization methods, and provides a detailed introduction to the melting pool dynamics anddefect evolution mechanisms during additive manufacturing. Finally, the future research trend of synchrotron X-ray imagingin the field of additive manufacturing is discussed.