Disadvantages of the active contour model with high computation cost, slow speed, and especially low efficiency are carefully researched and a novel active contour model is presented. The presented model replaces the real symbol distance function with the virtual symbol distance function, and the evolution of the active contour in presented model depends on the averages inside and outside the object. The gradient of the virtual distance function form a narrow band, where the active contour evolutes by simply adding and simply subtracting. Thus, the evolution has the following advantages: simple calculation, high-efficiency segmentation, free topology, and global property. The virtual symbol distance function is re-initialized with sign function after the virtual symbol distance function is regularized by the Gaussian function within a narrow band. In addition, a simple condition is given for the active contour convergence within the narrow band and it is easy to judge whether the object has been detected.