In this paper, the authors have studied systematically the complex stru- ctures of alkali feldspars of volcaniclastic rocks in the northeast part of iangxi province, mainly through X-ray single crystal analysis (including. precessioi. method, standard orientation oscillation method and Weissenberg: method)，accompanied' by X-ray powder diffraction, electron probe analysis. and complex struotural analysis. Ten kinds of diffraction patterns of single crystals were concluded and discussed (some of which have not been reported yet).With messages got from the study, the authors tried to infer the cooling history of the rocks. The alkali feldspars which have .side band diffraction and two phases (sodic and potassic phases) that are coherent were measured in order to determine the period of modulation (lamellar spacing) and the direction of exsolution. The structure of sanidine in one of the areas was also determined.