In view of the low efficiency in the prediction of the reliability of bolt connection by relying on few sample experimental data，based on GM(1, 1) prediction model，an optimization can be achieved from two aspects of the selection of original data and weakening treatment，and the prediction method of bolt connection residual preload has thus been proposed. Based on a case study of the bolt connection of current collector slide plate of the third rail train under lateral vibration，a verification can be achieved of the prediction method. The results show that，based on GM(1, 1) mean difference model，the prediction accuracy of bolt connection residual preload can be effectively improved by using metabolism method to select the original data，and then weakening the original data.