The invention provides a NaY molecular sieve and a preparation method thereof. The preparation method comprises the following steps: firstly synthesizing a guiding agent, then preparing a mixture for synthesis of the NaY molecular sieve, and finally adding a surfactant into the mixture and synthesizing the NaY molecular sieve with average particle size of 100-1000 nm by a hydrothermal crystallization method. The molecular sieve has high dispersity.