The multi-layer materials of metal and metal bonded structure are widely used in the fields of aerospace and nuclear industry. Due to its complex structure

it is difficult to detect the defects. This non-destructive testing（ NDT） system uses eddy current lock-in thermography method. The excitation source enlarge lock-in signals

which is used to drive the coil. The distribution of temperature on the surface of material is recorded by infrared（ IR） camera and the sequence of infrared images are transmitted to a computer for signal processing to acquire the phase and figure

which is used to defect the disbanding detection of lead-steel samples

and this method is compared with the nondestructive detecting method of eddy current pulsed thermography（ ECPT）. The experimental results show that the system has good signal-to-noise ratio and can be applied for defect detection of metal and metal bonded structures in practice.