In this paper, the detection of common defects such as inclusion, delamination for curved composite materials is studied. The principle of measuring porosity is focused on introducing. The technology of trajectory planning and motion control for twin-robot system of testing various curved composite parts using ultrasonic transmission method is also discussed. An ultrasonic NDT system is developed for testing large-scaled curved composite components used in aerospace and other fields. With many advantages, it will be very significant for our nondestructive testing work.