Because of the severe environments

in-service glass fiber reinforced polymer（ GFRP） composites is prone to exterior impact. And thus

thickness loss defect appears

which causes serious threats to the integrity and safety of structures. Therefore

it is indispensable to conduct effectively quantitative detection of the thickness loss in GFRP composites with non-destructive testing（ NDT） techniques. Microwave NDT for quantitative detection of the thickness loss in GFRP is intensively investigated. A 2D finite element simulation model for detecting GFRP thickness loss by microwave NDT method is set up and applied for analysis of the relationship between the detecting and response signal as well as its feature and the thickness loss defect. Ka-band（ 30～ 40 GHz） microwave NDT experimental platform is conducted. In experiments

an open-ended rectangular waveguide probe is used for 2D scanning imaging of defect

damage image is obtained. Experimental results verify the feasibility of quantitative detection of GFRP thickness loss defect in microwave NDT method.