In order to solve the problems of low testing efficiency and challenging quality control in the radiography testing process of a large-volume magnesium alloy casting with complex structure and large thickness variation，a set of automatic radiography digital imaging testing system was developed by using the design of planar array detector，small focus fixed X-ray machine，multi-degree-of-freedom C-shaped mechanical system，rotary testing platform，automatic loading and unloading system，etc.，and the detection test verification was carried out.The results show that the adopted radiography digital imaging testing process and the developed testing system can ensure that the quality of the detection image meets the requirements of the national standard，It can accurately detect the internal quality defects of the products，significantly improve the testing efficiency，and achieve the rapid and automatic radiography digital imaging batch testing of a certain type of large-volume complex structure casting.The testing method and system can effectively enhance the testing capability of products and provide a feasible reference for solving the radiography testing problems of complex structural castings.