Abstract: This paper improves Isomap algorithm,which is a nonlinear dimensionality reduction algorithm,and proposes a spatial alternation method based on metric multidimensional scaling.This method transforms road network distance in the original network space into approximate road network distance in a new Euclidean space,and then achieves Kriging based on this distance metric.The experiment of Nanchang's real data shows: this method has higher estimation accurate than Kriging based on Euclidean distance metric.Therefore,it is an effective solution to the problem of large-scale-road-network-level traffic state monitor.