Calcification of atherosclerotic plaque, which mainly observed in the intima of arterial vessels, is one of the clinical signs of atherosclerosis in cardiovascular diseases. Calcification in atheroma dose not increase the vulnerability of plaque, while microcalcification (μCalcs) located within the fibrous cap could intensify the background circumferential stress in the cap, resulting in increased vulnerability of plaque. The mechanisms of calcification in atherosclerotic plaques include passive calcification and active calcification. Passive calcification is regulated by hormones and local signals. The mechanisms of active calcification are a cell-mediated process, participated by matrix vesicles, cell apoptosis, exosomes, oxidative stress response and autophagy. This paper reviews the calcification mechanisms of atherosclerotic plaque.