In this paper, static-pressure strength, toughness index (TI) and thermal-toughness index (TTI) of each sample have been analyzed on the basis of the experimental studies on the magnetic separation and heavy liquid separation of diamond abrasives. The results show that the magnetism of synthetic diamond abrasives has an obvious influence on their mechanical performances. With the increase of magnetism, synthetic diamond abrasive particles becomes darker and darker in appearance color, and have more bubbles, impurities and defects inside the particles, furthermore, their surface fineness observed under the microscope will be found worse. While, the static-pressure strength, the TI under the normal temperature and TTI all become lower and lower. But the influence on the static-pressure strength and the TI is smaller, however the influence on TTI is the greater. The specific gravity of synthetic diamond abrasives has little influence on their mechanical performances.