Crop disease is one of the important factors that affect and restrict the development of agricultural production. How to accurately detect the cause and degree of crop disease, and realize scientific early warning and precise prevention of crop disease is particularly important. This paper firstly introduced the types of crop diseases, and then compared and analyzed the advantages and disadvantages of the biochemical detection technologies commonly used for crop diseases, such as molecular biology, immunology, and optical sensing detection technologies, and such as visible image, near infrared spectroscopy, infrared thermal imaging, hyperspectral imaging, etc. from the detection principle and mechanism. Through summing up, it was found that the difficulties of biochemical detection technology mainly included a large workload and a long cycle of detection and identification of a single target pathogen. The difficulty of optical detection technology included easy to be affected by the environment, the presence of foreign bodies in the same spectrum, etc. Finally, the future development direction of optical sensing technology in crop disease detection is given to provide a more comprehensive and systematic reference for related research.