A novel cooperative localization scheme for vehicular ad hoc metworks(VANETs) is proposed based on the semi-definite programming. Firstly, vehicles broadcast its movement information and exchange the range and angle data. The range and angle data are used to deduce simi-definite relaxation constraint condition for inter-vehicle distance matrix within a short time interval. And then the semi-definite programming method is employed to determine vehicles’ coordinate. Finaly, gradient descent optimization can be incorporated into our algorithm to further improve the estimating accuracy at the expense of additional cost. During simulations, the proposed algorithm is shown to provide preferable localization performance, and perform well on distance error.