To make an exploration with multi-robot system, it is important to calculate each robot's position, that is, to realize a localization. However, the growth of the number of robots will cause a computation explosion. Then, we proposed the simple localization method for a multi-robot system which consists of a big number of robot in our previous work. In this paper, we analyzed the error of the multi-robot localization with our proposed localization method. Especially, we analyzed not only the absolute distance error but also relative distance error and concluded that this method is successful whenever a small number of Land-Mark nodes are used.