It is urgent and important for online detection and evaluation of metallurgical quality during metal additive manufacturing in the aerospace field. The research status and progress of online ultrasonic testing technology of metal additive manufacturing at home and abroad were summarized. The design principle and the composition of the self-developed laser ultrasonic multi-metallurgical feature synchronous online detection system were introduced. The laser ultrasonic testing experiments were conducted using the self-developed system for the components manufactured by laser additive manufacturing. The size of coarse clusters of α-phase grains with preferred crystal orientation in laser melting deposited TC4/B4C composites was quantitatively evaluated based on the spectral centroid frequency shift of laser ultrasonic longitudinal wave pulse echoes. Then, the surface defects of laser melting deposited AlSi10Mg aluminum alloy were detected. The signal-to-noise ratio of the online real-time detection signal was improved by combining two methods. First, multiple laser pulses were excited at each measuring point in the scanning detection for averaging. Second, the twostep denoising method by combining the improved wavelet threshold and with variational mode decomposition was used. Based on the energy variation of surface wave pulse signals, the hole with a diameter of 0.5 mm and the horizontal crack with the width of 0.5 mm were imaged.