Balin Dam break cause the sediment goes down, and the upstream channel severe erosion. This is a big concern about head-cutting behavior after Balin dam break. Balin Dam is a 38 m-height dam, which is one of the dams on the upstream reaches of Shihmen reservoir. Balin dam broken because of the ruin of dam foundation and damage by flood events. In this paper, we will focus on simulating upstream channel evolution by using a quasi-two-dimensional model (NETSTARS) and analytical solution to compare with field observation, further to explain the river-bed evolution after Balin dam break. Owing to the transition of flow situation and severe landform variation, the output of model will be shaken. In case the simulation is more meaningful, choosing a stability index not only to evaluate the output of model, but also to estimate the river bed stability. In addition, Diffusion equation is developed as an analytical solution of riverbed evolution model so as to explain here the river bed evolution hourly after Balin dam break. Furthermore, to evaluate the head-cutting behavior by observing the motion of knick-point (or erosion threshold position) and finally find out head-cutting behavior is a power-rule distribution.