There are two types of alkali feldspars coexist in the syntexis type Tongcheng-Lujiang complex; one is colourless and transparent and the other is reddish in colour. A comparative study of structural state, composition, and exsolution microstructure was done for such alkali feldspars by using XRD, EPMA and TEM. The results indicate that the colourless and transparent one is sanidine with homogeneous exsolution microstructure and the reddish one is orthoclase or sanidine without exsolution microstructure. These two types of alkali feldspars have similar compositions. In principle, there should be a continuous range of Al and Si ordering with decreasing temperature, from completely disordered high sanidine to completely ordered low microcline. In the Tongcheng-Lujiang complex, the varying trends of Al and Si ordering of the two types of alkali feldspars are different. As the cooling rate of magmas varies from high to low, the Al and Si ordering tends to increase for the colourless and transparent alkali feldspar and decrease for the reddish one. This is obviously contradictory to previous results (Stewart et al. , 1974; Deer et al. , 1992). In the present paper, the authors discuss the genesis and petrologic significance of the coexisting alkali feldspards, which can provide evidence for the mixing of magmas in yhe Tongcheng-Lujiang complex.