In this paper, we present an algorithm to compute the distance to uncontrollability. The problem of computing the distance is an optimization problem of minimizing [sigma](x,y) over the complete plane. This new approach is based on finding zero points of grad [sigma](x,y). We obtain the explicit expression of the derivative matrix of grad [sigma](x,y). The Newton's method and the bisection method are applied to approach these zero points. Numerical results show that these methods work well.