Abstract: Ziplock snake, ribbon snake and quadratic snake are three classical snake methods applied in roads extraction. The quadratic snake is the most complicated the least accurate among the three. Having better outcome however, the ziplock and ribbon snake methods need the initial road information provided by other algorithms. Once some part of the initial road network is missing, it cannot be recovered by the ziplock or ribbon snake. In this paper, the balloon snake with adjustable expansion coefficient is adopted. Its advantages include: 1. with the introduction of expansion force in the balloon snake, the missing road parts can be recovered; 2. expansion coefficient tuning according to image gradient and contour curvature solved the problem of the output’s sensitivity to the coefficient. The experimental results demonstrate its effectiveness and advantage.