Granitic rocks of different ages are extensively distributed along the Gandes Chain. They are intimately genetic related both in origin and is space. The rocks consist mainly of diorites, granodiorites and granites, with the predominance of granodiorites in this granite belt. In general, their distribution has a tendency to change rocks nature from basic to acid from south toward north. The optical properties of feldspars indicate that alkali feldspar ordering shows itself a systematical increase along this direction just as the changes of host rocks in composition of SiO2, K2O and the volatiles. The variation of An component of plagioclase is also in comply with the decreasing of CaO, FeO + Fe2O3 and MgO of the host rocks. The ordering of alkali feldspars generally can be regarded as a complex function of chemical composition of host rocks, the dimension of rock masses and the amount and component of volatiles. Among them, it is believed, the last one is most important especially for boron. Obviously the types of rocks could play an important role to the An content of plagioclases.