A method for automatic defect inspection in wheel shaped casting products is provided, and the three major phases contain preprocessing samples, offline training and online inspection. Specific steps include: collecting and preprocessing training samples, dividing them into three kinds of spoke, rim and axle samples; offline training with the aforementioned three kinds of samples, then generating online detectors respectively for spokes, rims and axles; uploading the well-trained spoke, rim and axle CNN defect detector to the upper computer, placed it in automatic production inspection line. Inspect for defects online automatically. The defect inspection system outputs signals according to the user's requirements. The present invention has a high level of accuracy and reliability, and a strong robustness to variations in illumination, shooting angle and the position of the work piece. It delivers a high level of automation and has no need for an operator to adjust any significant parameters.