The invention provides a synthesis method of a ZSM-5 molecular sieve. The synthesis method comprises mixing a modified filtrate, a silicon source, an aluminum source and a template, and carrying out crystallization on the mixture, wherein the modified filtrate is obtained by anion exchange resin-based exchange of the ZSM-5 molecular sieve crystallization filtrate. The invention provides the ZSM-5 molecular sieve obtained by the synthesis method. The synthesis method realizes synthesis of high-crystallization degree, high silica-alumina ratio and low sodium content ZSM-5 molecular sieve from the crystallization mother liquor.