The invention discloses an online measuring device for size and morphology of a particle. The device comprises a full-automatic sampling system, a diluting system, an online observation system, an image processing system and the like, wherein the sampling system comprises a peristaltic pump and a feeding tube and is used for conveying an obtained sample to the diluting system; the diluting systemcomprises a liquid storage tank and a diluting tank and is used for diluting the sample to a concentration suitable for the observation of the online observation system; the online observation systemcomprises a high-definition camera or a microscope, an observation table and a computer; the sample conveyed to the observation table is photographed in real time by the high-definition camera or themicroscope and stored on the computer; the morphology and the size of the particle can be observed in detail through a computer program; the image processing system is an image processing program withindependent intellectual property rights; and the program is used for processing pictures taken by the high-definition camera or the microscope in real time and obtaining the size distribution and the specific morphology features of the particle through data statistics.