A kind of double microporous 
zeolite and preparation method thereof belong to the technical field of 
fine chemical industry, it is characterized in that adopting two-step 
crystallization method, the first step first synthesizes Beta, then with the synthetic Beta reaction mixture as the 
raw material of the second step synthesizing Y 
zeolite,  The composite 
zeolite product with BEA / FAU structure is obtained by supplementing the aluminum source, adjusting the basicity of the 
system, adding the directing agent for synthesizing Y zeolite for reaction 
crystallization, filtering, washing, 
drying, and calcining.  The method successfully solves the problems of pouring part of the 
clear liquid and difficult control of the amount of aluminum source and base added in the synthesis because the 
clear liquid contains components such as 
silicon, aluminum and alkali, and the product 
repeatability is difficult to control.  The synthesized Beta / Y composite zeolite products can be used as various catalysts, catalyst assistants and adsorbents. After 
ion exchange, they have strong acidity and good thermal and hydrothermal stability. They can be used as various catalysts, catalyst assistants  It is bound to have potential application value in catalytic 
cracking and hydrocracking of 
petrochemical industry.