Abstract: The laser deep penetration welding monitoring systembased on the virtual instrument technology was introduced. The component of hardware and the development of software were illuminated. Three signals of ultraviolet light, infrared light and acoustic signal acquired by three special sensors. The raw data were processed dy DSP, multi-sensors data fusion was done by neural network algorithm, and the reliable result of welding quality was oslained. The experimental data proved the system ' s validity and stability.