under a set of assumptions, Maximum likelihood estimation method is analyzed and simulated to make wireless sensor network's localization more accurate. The result shows that, the range error between the anchor node (we call it the reference node) and the unknown node contained in the nth equation (we call it the reference equation) and the position of the reference node has significant impact on the node localization. The result of the simulation shows that if the range error contained in the reference equation can be reduced more, and the position of the reference node is appropriate, the localization error will be smaller.