Abstract: This paper describes a solution for improving the dynamic range of vector network analyzer, in this solution, Narrow-Dither technology is used to the receiver of vector network analyzer, raising the spurious free dynamic range of the analog / digital converter (ADC) of the receiver effectively. This paper not only gives the reason for adopting this solution theoretically, but also describes the function and implementation of each module.And finally, proves the feasibility of this solution by the test result of vector network analyzer.