Taking full coring ZK4704 as study sample, located in the southern margin of the North China Craton, Yanlong area, Western Henan, through core observation and vertical continuous sampling, the mineralogical characteristics and vertical varying pattern of bauxite mineral have been analyzed by rock thin section, SEM, EDS, Xray diffraction, as well as differential thermal and infrared spectrum. The results show that all the minerals in Albearing rock series in Benxi Formation are authigenic minerals mainly existes in cryptocrystalline or microcrystalline except those affected by recrystallization during late stage. The mineral compositions and assemblages show significant variation in the vertical. Minerals in the lower and upper mudstone mainly are clay minerals. But the lower mudstone mainly consists of Illite, and the upper mudstone mainly consists of Kaolinite. Mierals in the middle between lower and upper mudstone mainly consist of aluminum minerals with a small number of clay minerals. On the basis of above, taking the basic principles and generation conditions of chemical weathering as the link of mineralogical characteristics of Albearing rock series and raw rock to analyze the original rock of bauxite, it is theorized with a high degree of probability that the Albearing rock series in Benxi Formation might be volcanic ash which could be rapidly hydrolyzed, the change of hydrolysed chemical environment can be explained by the transformation from weakly alkaline marine environment to weakly acid marsh environment, the strongly karstification of the basement under Albearing rock series provided well drainage condition for the formation of diaspore. Violent volcanic process in the northern margin of the North China Craton and China's western region can provide ash provenance of Benxi Formation in Yanlong area.