Open clusters are good tracers for the study of the structure and evolution of the Milky Way. Previous studies of open clusters have shown that only a small number of open clusters have metallicity measurements. Moreover, these measurements based on different qualities of observed data, using different methods. In this paper, we collected a sample of an elderly open cluster older than 2Gyr by collating the metallicity data of these cluster members. On the one hand, the systematic errors of metallicity of members given by different spectral survey projects are compared as the example of NGC 2682. On the other hand, the mean and median values of metallicity of the members are calculated as the recommended values of metallicity of the open cluster. In addition, the evolution of the radial metallicity gradient of the disk with time was investigated using this sample. The results show that the radial metallicity gradient of the disk is steeper in the early stage, and gradually becomes flat with the increase of evolution time, which provides a more strict observation constraint for the chemical evolution model of the disk.