Considering laser scanning technique, IR method and electronic technology, studied and design a set of IR NDT system with laser scanning automatic, heat loading method in this paper. To make use of this device, it may detect internal defects of metal material parts, such as micro- craze, refraction, blowholes, etc. This paper also introduce the work principal of testing system. It heats automatically pretreatly to workpiece with CO2 laser scanning and through IR technique received temperature field from workpiece heat conduction. After the filter and the A/D converter system, the changed signal is sent into a single chip computer and the computer make it complete data analysis, data processing, save and display. Therefore, it can achieve detecting characteristic and property of internal defects of parts.