Abstract: The 21st century has witnessed the rapid development of digital signal processing technology. A significantly increasing amount of electronic equipments, including GNSS receiver, select to process the data in digital domain, as it’s more convenient for both software-based simulations and hardware integrations than in the analog domain. The fundamental processing of ADC would more or less bring inevitable signal loss. And we have different requirements for the accuracy corresponding to different standards. In the paper, a precise deducing about the changes of effective information of the navigation signal and signal-to-noise ratio is given, theoretically confirming that an ADC in 2 or 3bits would meet most of the requirements in general receivers. Furthermore, the different influences, determined by the chosen AD threshold, are elaborated too. One result shows that in some very kind of interference, the signal-to-noise ratio increased after the ADC, which is profitable for the ensuing processes thought not agreeing with the common sense. Finally a solution of how to choose the AD threshold in the GNSS receiver so as to get a most gain (a least loss) is demonstrated, which has been proved by the simulation in Matlab project.