In local area augmentation system,the quality monitoring of measurement data is necessary for system integrity monitoring.The way of quality monitoring is comparing the observations collected with corresponding thresholds,and then decides if a failure is happening.Proper valued thresholds are usually the key to achieving the desired performance of the integrity monitoring.This paper proposed a Gaussian overbounding method to determine thresholds.The requirement of false alarm probability of the system is considered,and the threshold is calculated from a Gaussian distribution thatoverbounds the two tails of the probability density distribution of the observation data.Comparing to the threshold determination methods depending on engineering experience or threshold models,this method satisfies the requirement of false alarm probabilityof the system; moreover,it accords with the real characteristic of the system due to the thresholds are calculated using own observation data of the system.