The invention discloses a crop lesion detection method and device. The detection method comprises a lesion classification step and a lesion recognition step. In the lesion classification step, training of a decision tree classifier is completed according to lesion type labels and image features of all sample images; and a plurality of feature template images are generated according to the decisiontree classifier; the lesion identification step comprises the step of calculating the matching degree between the to-be-detected image and each feature template image by using a semi-naive Bayes classifier; and judging possibility of lesion of to-be-detected crop according to the matching degree between the to-be-detected image and each feature template image. According to the lesion detection method, in the lesion classification step, a decision tree classifier is used for determining crop characteristics corresponding to various different lesion types, so that a template image is generated;in the lesion identification step, the matching degree of the to-be-detected image of the to-be-detected crop and each template image is calculated by using the semi-naive Bayes classifier, so that the lesion type of the to-be-detected crop and the possibility data of the lesion are obtained, and the reliability is high.