Critical dimension analysis of cross-section image with delicate accuracy has become important demand for semiconductor manufacturing. In traditional analytic method, manual measurements always accompany large deviation and lower measured efficiency. Therefore, a robust and reliable analysis method is most essential objective to obtain accurate dimensions from PFA results. In this work, we demonstrate an intelligent image analysis method which is combined Mask Region based Convolution Neural Networks (Mask r-CNN) and image processing technique. Compared with manual measurement, intelligent image analysis method can achieve significant improvement on measured results in reproducibility, repeatability, and efficiency. This intelligent image analysis will provide novel applications in CD measurement, wafer defect analysis, and focus-exposure process window judgment.