In aeronautic industry, more efficient and accuracy non-destructive test methods (NDT) are required to critical parts test. Different techniques are nowadays used, but one of methods most suitable to automated test is ultrasonic testing. When performing non-destructive testing of aerostructures with complex geometrical shapes and curved surfaces, two problems arise: one is generation of an appropriate sequence of 3D coordinates and orientations for the test probe to follow complex component contours; the other is interpretation and characterization of defects based on 1D、 2D or 3D NDT data.In this paper, combining with the national defense prototype project "multi-freedom degrees ultrasonic detection system" and some technique reconstruct project for national defense prototype, takes the large parts with complex geometries and composite materials in aeronautic industry as research object, takes the automatic ultrasonic testing as research content, aims to the enhancement of the precision, efficiency and automation. The theory 、 experimentation and the development of equipment for the test of parts with complex geometries. Theory, method, experiment and system implementation related to automatic ultrasonic testing of large parts with complex geometrical shapes and curved surfaces are researched in terms of "building one system, analyzing two aspect and study on three key technique".Firstly, a general research frame of NDT system for complex geometry parts is proposed and is applied to NDT for large complex geometry composite structures in aeronautic industry. An integrative strategy of ultrasonic testing with path control and data interpretation automatically is proposed. Experiments show the strategy can improve the precision, efficiency and automation obviously, and it is worth generalizing.Secondly, using type, property of acoustics test, main factors influencing the ultrasonic testing, possible methods of ultrasonic testing and methods of data sampling are analyzed systematically and closely. For the first time, implement of automatic ultrasonic testing system for large parts with complex geometries and composite materials is analyzed, including the assembly of system, numerical control system integrated with IPC and Programmable ultrasonic card, numerical