Maximum likelihood estimation method which is now widely used is analyzed through some experiments.The results show that the ranging error and the position of the anchor node

which is called reference node

contained in the reference equation（the n th equation）have significant impact on the node localization with Maximum likelihood estimation method:the smaller the ranging error of the reference node is

the more accurate the node localization will be.When all the equations have the same ranging error in this method

the localization error is relatively smaller if the reference node is in the center of the position area

but bigger on the edge.When the ranging error in the reference equation is 0

the location estimation error is relatively bigger if the reference node is in the center of the localization area

but smaller on the edge

whereas

there is no significant difference between them.In the real application

the node localization can be optimized by choosing an appropriate reference node with these results.