The dark- colored microgranular enclaves often occur in calc- alkaline granites, and have been considered to be product of magma mixing between mantle- derived basic magma and crust- derived acid magma in deep crust. After analysis on a large amount of documents, it is found that the dark- colored microgranular enclaves could show very negative whole- rock εNd（t）values and zircon εHf（t）values, and whole- rock \[n（87Sr）/n（86Sr）\]i values of more than 0. 710, thus indicating no mantle- derived magma. In addition, most dark- colored microgranular enclaves and host granites are very similar in crystal chemistry, formation age, and isotopic composition of zircons, reflecting that both are congenetic based on their temporal—spatial and material relationship. This paper considers that the dark- colored microgranular enclave could not be regarded as product of crust—mantle interaction. On the basis of very small volume and a little later emplacement of magma of the dark- colored microgranular enclaves (relative to the host granites), this paper proposes a new formation mechanism for the dark- colored microgranular enclaves: the forceful emplacement of syn- orogenic granitic magma caused “negative pressure” in magma chamber, which resulted in isothermal decompressing melting of the dioritic layer in the form of crystal mush and located in lower part of magma chamber, and formation of a small volume of magma of the dark- colored microgranular enclaves; then, the latter injected into unconsolidated host granitic magma in upper crust and rapidly crystallized and formed the dark- colored microgranular enclaves. Therefore, the dark- colored microgranular enclave could not be regarded as the evidence for magma mixing under crust—mantle interaction.