In this paper,we devote to develop a high order semi-implicit time discretization method for highly nonlinear PDEs.These PDEs are highly nonlinear,fully implicit method will incredibly increase the difficulty of implementation.In particular,we can not well separate the stiff and non-stiff components for these problems,which makes the traditional implicit-explicit methods nearly meaningless.We couple the semi-implicit method with LDG method to obtain high order accuracy both in space and time.