The rice husk ash (RHA) from biomass gasifiers was hydrothermally reacted with KOH solution to obtain the RHA ludox, which was used to synthesize K—ZSM—5 zeolite by hydrothermal crystallization. The effect of hydrothermal reaction time on the Si dissolving rate was investigated, and the complex composition of the RHA ludox was analyzed as well. The effects of template types, Si/Al molar ratio, crystallization temperature and time on the nucleation and growth of K—ZSM—5 zeolite in the complex RHA synthesis system were studied. The as-synthesized samples were characterized by XRD, SEM, ICP, TG, N2 adsorption-desorption and other means. The results showed that the structural directing agents with strong template effect were necessary to synthesize K—ZSM—5 zeolite directly using the RHA ludox. The zeolite crystals could not be prepared by the weak organic template as ethanol, however, using little TPABr strong template, the K—ZSM—5 zeolite crystals could be synthesized with a certain range of the Si/Al molar ratio. But there were some disadvantages such as the narrow adjustable range of synthesis solution, irregular crystal shape, large grain size, high synthesis temperature, long reaction time, and so on. It was also found that the calcination methods had great influence on the pore structure of large K—ZSM—5 products. It was easy to form deposited carbon over the zeolite crystals that were directly calcined at 550℃. To obtain pure K—ZSM—5 products, it must be calcined at 350℃ for 3 h before high temperature calcination at 550℃.