The non-contact ultrasonic Lamb wave method can detect the large area composite sheet quickly and has the outstanding advantages in the automatic imaging detection. A0 mode lamb waves were excited by air-coupled ultrasonic probes for carbon fiber reinforced resin (CFRP) composites laminates. The Lamb waves were scanned and detected on the same side of the sample with the impact damage, and the Lamb waves were scanned in two directions which are orthogonal to each other to obtain the detection signals at different positions. Based on the characteristics of the Lamb wave propagation signal in the without defects and with defects plates, the frequency domain analysis of the acquisition signal is carried out. It is caculated for signal difference coefficient (SDC) based on no defects area signal.And SDC is used as characteristic value, the scanning imaging is achieved form characteristic value by using full summation algorithm and full multiplication algorithm data fusion method. Contrast of the amplitude imaging scan,the SDC imaging results are able to reflect the position of impact damage more,and it can show the impact size in two directions.