Abstract: Laser processing technologies can be categorized into two modes: conduction and keyhole mode. In particular, the keyhole effect generated during the keyhole-mode processing significantly enhances the efficiency of laser energy utilization. However, this process involves the transient multiphase coupling of solid, liquid, gas, and plasma (plume) phases, rendering it highly susceptible to defects such as spattering and porosity. These defects severely limit the broader application of laser manufacturing technologies. Addressing this bottleneck necessitates an mechanistic understanding of the dynamic keyhole evolution. Compared with conventional monitoring techniques, such as visible light and acoustic signals, X-ray imaging, owing to its strong penetration capability, provides a novel approach for in-situ observation of internal dynamic processes within materials. This review focuses on three key aspects: keyhole initiation, dynamic behavior, and stability control, and summarizes the latest research progress in the field of keyhole-mode laser processing. Furthermore, it outlines the classification and underlying principles of X-rays, and offers perspectives on future opportunities and potential challenges in this field.