Abstract: From the point on economic value of diamond, it is the very expensive gemstone; from the point on science mining, it is a window to provide the physical states and chemical compositions of mantle. The nature occurrences of diamonds, the forming condition, its impurities, the feature of varied inclusions, and the origin model of diamonds have been introduced briefly. The major host rocks are peridotites and eclogites. Syngenetic inclusions in diamonds can offer the important evidences on the composition of host rocks, P-T condition of diamonds and residence ages in mantle of diamonds. In the last two decades ultra deep mineral assemblages as inclusions in diamonds were discovered and they may come from transition zone and lower mantle. According to this discovery diamonds are perhaps the unique window to recognized whole mantle.