The impact damage features of carbon fiber laminated board were extracted by double-side pulse thermography non-destructive testing method. According to the infrared image sequences,the curve of temperature difference between damage regions and reference regions with time was analyzed,and the optimal infrared image was selected through the maximum gradient value of the curve rising edge. The impact damage of carbon fiber laminated boards was detected by ultrasonic C-scan,and infrared images at the curve rising edge and ultrasonic C-scan image were processed by Image j to obtain the impact damage features of carbon fiber laminated board. Then the impact damage area error in infrared images was calculated compared to ultrasonic C-scan. Finally,the impact damage area error was analyzed according to the gradient of curve rising edge. The results show that the impact damage area error of infrared image is minimum when the gradient of rising edge curve is maximum. The farther away from the maximum gradient,the bigger is the impact damage area error. This illustrates that the method which selects the optimal infrared image from infrared image sequences based on the maximum gradient in curve rising edge of temperature difference is feasible.