Wireless Mesh Networks (WMNs) is a promising network access technology. As WMNs’ applications become more and more popular, the number of users grows quickly and the quality of service needs to be improved. When we try to analyze the load on different paths using the simplest multi-path routing algorithms we find that the load changes just like Simple Harmonic Motion, which inspires us to use physic model to analyze the traffic allocation problems. And then we design a new traffic allocation algorithm and the experiment shows that the algorithm can reduce the path delay variance.