High-speed digital-to-analog converters (DACs) are core components of microwave return systems and radar jammer signal processing units. In the aerospace environment, they are highly susceptible to radiation, which can lead to functional abnormalities. Due to their extremely high interface data rate, evaluating single-event functional interrupts (SEFI) presents significant challenges. This study investigates and analyzes four types of single-event functional interruptions in high-speed DACs in heavy ion environments. A single-event functional interrupt ground simulation testing method for JESD204B interface DACs (≥12 GS/s) is proposed. Additionally, a single-event functional interrupt online testing system for JESD204B interface digital/analog converters, based on the current steering structure, is designed and implemented. Experimental verification was conducted at the HI-13 and SESRI facilities, successfully monitoring the single-event functional interrupt phenomena, which were consistent with the device structure mechanism analysis. This work provides valuable guidance for subsequent reinforcement design.