Abstract: According to GIS data of manual digitizing map,this paper uses coordinates of the same name point on multi-lift overlay to estimate uncertainty of the position data and gives a calculating method.Its main contents include using testing method of dual sub-sample array to do gross error testing to manual digitizing data of two-lift overlay,and giving the synthetic estimation method of unit weight variances.The characteristic is the application of the principle of statistical test and statistical estimation brings a more reasonable and simple result.