The design of wide angle X-ray supermirror, wide band-pass multilayer optical elements operating in the hard X-ray region is attributed to the global optimization of the multi-dimensional extremum of continuous variables. Lack of powerful optimization method is the key obstacle to this problem. Simulated annealing algorithm is a simple and universal global optimization method. Based on the theory of optical multilayers, a new method of designing wide angle X-ray supermirror using simulated annealing algorithm is presented. The coating materials pair W/C is selected by the combination of the Spiller' and Yamamoto' criterions. The designed supermirror with high and flat reflectivity of 20%, over a grazing incident angle range 0.9°～1.1° at the wavelength of Cu Kα line is completed. Furthermore, the improved adaptive simulated annealing algorithm is used to obtain a better design result. The validity of the proposed algorithm is shown by the example involving multilayer design.