QoS routing based on node-delay information is an active research area these years. When delay is used as node state, it is often assumed that the state between each node is independent. Node-State independence assumption can provide a more tractable solution to delay constrained routing, especially when state information is Probability Density Function (PDF) of delay at each node. In this paper, the effectiveness of node-state independence assumption in Autonomous Systems with limited node number is investigated, and the conclusion is verified through vast simulation, whereas 60 link-delay PDFs and 15 path-delay PDFs in the network are observed. The 15 path-delay PDFs are also calculated by convolving the PDFs of contributing link-delays based on independence assumption. The statistical distance between the two sets of path-delay PDFs is measured by calculating divergence and comparing their delay expectation, variation and loss probability. Simulation and analysis results indicate that for Autonomous Systems with limited node number, node-state independence assumption is reasonable and path metrics calculated based on this assumption approximates well the original values and can be used in QoS routing.