Abstract: The reinitialization process is quite time-consuming in level set method. A new variational formulation which is the difference between the level set function and the signed distance function is introduced to C-V model. In this way, the level set function is forced close to a signed distance function, and therefore completely eliminates the need of the constly re-initialization procedure. Also, when detecting more than one object, a group of curves are choosed to be the initial curve. In the numerical implementation, AOS scheme is adopted to eliminates limit of time step. So the large time step can be selected to accelerate the evolution velocity. The result shows that the evolution velocity is greatly improved and the precision doesn't reduce.