Infrared thermography is a fast and effective non-destructive testing(NDT) method which has been widely used in the fields of aerospace,rail transit,nuclear and etc.The excitation source is a crucial device for the optical thermography system whose performance has an impact on the test results.There is a limitation of gain bandwidth product by using linear amplification to generate excitation,and it is difficult to meet the requirements of frequency range and high power.In this paper,the voltage is modulated in a digital way to achieve a higher power output and improve the efficiency of defect detection.In order to meet the requirements of power,frequency and multi-mode,an excitation source for the infrared thermography based on FPGA is designed.The excitation source includes the low-frequency sinusoidal generating circuit,full-bridge chopper circuit and FPGA control system,of which the control part is the focus.Experiments′ results show that the excitation source can realize two modes of excitation(pulse mode and lock-in mode),and be easy to adjust,and meet the requirements of infrared thermography on the excitation source.