It is very important to understand the field distribution of pesticides by quickly obtaining the deposition distribution of droplets on the surface of water-sensitive paper(WSP) after spraying pesticide. At present, the water sensitive paper image processing software lacks the pre-processing operation such as the rotation of the water sensitive paper image, also it has the low detection accuracy problem which is caused by converting the water sensitive paper images to grayscale images before segmentation. To address these shortcomings, a water sensitive paper image processing software based on ImagePy is developed in this paper, by which the droplet size and distribution characteristics of water sensitive paper can be quickly and accurately detected. The software consists of a group of user-defined plug-ins, which can automatically detect and rotate the water sensitive paper images, and then, color image segmentation is done for water sensitive paper images. Further, the droplet parameters such as droplet size, distribution, total droplet number and droplet density can be measured by these plug-ins. Finally, the measure results are saved in Excel for subsequent data processing. The effectiveness of the software is verified by comparison with the DepositScan software.The experimental results show that the method of image preprocessing and droplet parameter measurement based on Imagepy can extract more than 94.1176% of droplets on the test paper, and the accuracy rate is 6.7707% higher than that of Depositscan software.