Biodiesel and regular diesel in any proportion miscrible mixtures can be used instead of petrochemical diesel fuel for internal combustion engine. In order to make the mixture in internal combustion engine applications to achieve good effect on performance and emissions, we need to research different proportions of biodiesel-diesel mixture atomization effect. In this paper, digital image processing methods is used for biodiesel-diesel mixture atomization image processing, to obtain the number per unit area and the average diameter of atomization particle, fast processing speed, accuracy, reducing the traditional manual method of analysis of subjectivity and a higher failure rate.