The invention relates to the field of pesticide spraying effect detection, and particularly discloses a plant protection fog drop detection method based on an HSV color model, which comprises the following steps: firstly, extracting an R channel image of a fog drop picture, processing the R channel image by using an HSV color model masking method, filtering redundant background information, binarizing to obtain a fog drop contour binary image, extracting the fogdrop contour after morphological denoising and opening operation denoising, finally, calculating the fogdrop contour surrounding shapearea, filtering redundant interference information, and acquiring a fogdrop detection result. According to the method, R three channels are combined, the HSV color model is used for generating the mask map, the mask method is used for detecting the fog drops, and important technical indexes such as the fog drop number pitch diameter, the volume pitch diameter, the deposition density and the deposition coverage rate for measuring the pesticide spraying effect can be accurately counted on the water-sensitive paper with dense fog drops. The detection process is simple.