Mantle fluid metasomatism in the deep geologic process is an important substance supplier and energetic contributor and the complexity of its nature and evolution make it difficult to be observed and confirmed. Based on the researches of petrography, petro-chemistry, electron microprobe (EMP), scanning electron microscopy (SEM) and energy spectrum (EP), it is discovered that there are two kinds of the actual microcosomic traces of mantle fluid, that is Fe-rich melt xenolith and Fe-rich microglass. Both are of non optics under transmitted polarized light appearing to be black opaque and can not reflect light under the reflected polarized light. EMP results show that the Fe-rich melt xenolith and Fe-rich micro-glass are of micro-crystalline texture and unmixing texture composed of micro-metals and micro-nonmetals. The micro-minerals are mainly silicates and quartz, and after the ratios calculation we get the SiC, Cr-bearing natural iron, ilmenite, apatite and Cr-bearing specularite and all of these are indication minerals of mantle, suggesting the nature of mantle fluid be similar to the melt. The study of the actual microcosomic traces of mantle fluid in deep geologic process is of high significance to the mineralizing mechanism in the Earth’s Crust.