Pore defects in metal laser additive manufacturing (AM) typically originate and evolve within the melt pool, exhibiting microscopic and highly transient characteristics. High spatiotemporal resolution X-ray imaging provides a powerful tool for in situ characterization of these processes, which is essential for understanding defect formation mechanisms and optimizing processing parameters. In this study, a high spatiotemporal resolution X-ray imaging technique tailored for metal laser AM was developed utilizing Betatron radiation generated by an ultra-intense, ultrashort pulsed lasers. This technique was employed to perform in-situ characterization of micro-melt pools under various processing conditions. The results show that the Betatron X-ray source allows real-time imaging of melt pool and keyhole dynamics in metal samples with thicknesses on the order of hundreds of micrometers, achieving a spatial resolution of 4 μm. These findings provide a solid foundation for the future application of laser-driven X-ray sources in investigating defect formation mechanisms and advancing process optimization in metal laser AM.