The invention discloses a preparation method of a mesoporous-microporous composite 
molecular sieve. The preparation method comprises the following steps of adding a microporous 
molecular sieve subjected to 
hydrothermal treatment into a mixed 
system of a 
silicon source, an acid solution and a surfactant, then carrying out 
crystallization, 
filtration and washing, and then carrying out 
drying and 
calcination to obtain the mesoporous-microporous composite 
molecular sieve. The preparation method fully utilizes non-framework aluminum falling from the microporous molecular 
sieve, avoids an aluminum source used by the conventional molecular 
sieve preparation technology, is conducive to improvement of a silica-
alumina ratio of the mesoporous-microporous composite molecular 
sieve, realizes a high degree of 
crystallization, and improves hydrothermal stability and 
thermostability of the mesoporous-microporous composite molecular sieve. The mesoporous-microporous composite molecular sieve is suitable for the field of 
macromolecule catalysis, is conducive to improvement of a reaction conversion ratio and reaction selectivity, and is especially suitable for being used in a 
cracking catalyst for maximum-degree production of middle distillate from heavy oil as a 
raw material.