The image-based approach used to evaluate inline mixing efficacy for the pesticides mixers has advantages of not disturbing flow fields and achieving convenient and quick uniformity evaluation. Inline mixing tests for a jet mixer were carried out by using plastic particles to simulate water dispersible granules (WDG) pesticides. Distribution of particles flowing in the detectable region of the mixer was collected with the help of a high-speed camera and a total reflection prism to receive images from both horizontal and vertical viewing directions. For the acquired images, the particle images were pre-processed based on the morphological method, and segmented by the iterative thresholding method. Then, the particle center of gravity coordinates and normalized moment of inertia (I) parameters were extracted from each image in two viewing directions. The particle matching and 3D reconstruction based on the multi-viewing images were realized according to the consistency of the corresponding particle abscissa. The method for calculating the uniformity of the particle spatial distribution was proposed. Furthermore,according to the reconstructed three-dimensional images,the matching of the particles between frames was completed, and the calculation method to obtain the particle velocity distribution and measure the performance of the mixer was proposed. The actual verification results of the four kinds of plastic particles used to simulate WDG of differing physical properties by the above method showed that the particles with lower sedimentation velocity (caused by small particle diameter and density similar to water) under the condition of horizontal placement of the mixer led to high mixing uniformity. Accordingly, they did not tend to have downward velocity vectors, which allowed the actual WDG to have uniform distribution after dispersing and dissolving, and sufficient mixing efficacy.