Line laser scanning thermography is a nondestructive testing technology that uses a line laser as a thermal excitation source and adopts a scanning heating method. It has unique advantages in the nondestructive testing of carbon fiber composites. Here, three parameters that may affect the detection, namely, scanning direction, scanning speed, and laser power, were identified by analyzing the line laser scanning thermography technique and characteristics of composite materials. A simulation model for the detection of composite materials using line laser scanning was established, and the maximum temperature difference between the center point of the defect surface and surface temperature of the defect-free area was selected as the characteristic quantity for detection. The influence of the above parameters on detection was analyzed, and the relationship between the laser power, scanning speed, and detection was fitted. Based on this, the principle of parameter selection considering detection efficiency during the experiment is summarized.