The invention relates to the technical field of the welding line defect nondestructive detection, and especially relates to an actively-motivated welding line defect infrared intelligent detection system and method. The infrared intelligent detection system for welding defect detection is composed of a driving device, a regulating device, a high-definition camera, an upper computer, a signal generator, a laser pulse gauge, an infrared thermal imager and a code-spraying mark device, different types of welding slot defect can be detected, the infrared intelligent detection system of the welding slot defect can acquire a welding slot trend through the high-definition camera, the laser pulse gauge is used for emitting active laser pulse to perform thermal excitation on the welding slot region, the infrared thermal imager acquires an infrared thermal image, an upper computer system performs image processing on the infrared thermal image, and distinguishes the welding slot defect in real time, and the code-spraying mark device is controlled to automatic identify the welding slot defect location. The intelligent continuous detection of the welding slot defect can be realized, all welding slot defects can be effectively distinguished, and the system has the features of being energy-saving and environment-friendly, efficient and accurate, intelligent and continuous and safe and reliable.