This paper used the image recognition algorithm model and Detectron2 framework to detect five types of defective Irwin mangos. The principal object was to recognize five different diseases concerning Irwin mangos by multi-object instance segmentation. There are five diseases respectively, poor coloration, anthrax, latex attached, mechanical harming and ink spot disease. We spent over 500 hours on data cleaning and data pre-processing due to the dataset (training set + validation set totally 59650 images) offered by vendor is inferior in quality. We also eliminated 8995 bad images. Finally, the dataset remained 50655 images. Data collection and data hazard are the significant challenges will face when apply AI to the real-world. Our research mainly used Mask R-CNN which is the image recognition algorithm of deep neural networks and transfer learning based on COCO Dataset Pretrained Model makes the detection results more precise. Then, we used Grabcut algorithm which makes accuracy of instance segmentation up to 99.9% in data pre-processing stage. Further, we applied X101-FPN backbone for making neural network deeper which compared to R50-FPN was effectively improved 90% accuracy. Eventually, we achieve the 67.2 AP in ours experiment.