The invention provides a mesoporous ZSM-5 molecular sieve and a preparation method thereof. The mesoporous ZSM-5 molecular sieve is prepared from natural mineral diatomite as only silicon source or expanded perlite as only aluminum source and has a mesoporous volume of 0.064-0.100cm<3>.g<-1>. The invention also provides a preparation method of the mesoporous ZSM-5 molecular sieve. The mesoporous ZSM-5 molecular sieve can be used in a cracking reaction. Because of abundant mesopores, in the reaction, a catalyst fluidization state is good, a heavy oil macro-molecule approaches to an active center easily, cracking products can be diffused easily, the catalyst has good catalytic activity, and ethene and propylene yields can be improved.