The invention relates to a multi-facility fair site selecting method. The method comprises the following steps of: calculating a shortest distance from all demand points to facility points and constructing a distance matrix; calculating a weighted average distance from each selectable facility point to all the demand points according to the distance matrix; constructing a matrix of a weighted distance variance between all the facility points and the demand points; constructing a fair site selecting target function according to a site selecting principle of selecting the facility point with the smallest weighted distance variance; solving the target function and finishing multi-facility fair site selection. The method and a system simplify the solving difficulty of the fair problem of multi-facility site selection, select by adopting an ant colony algorithm, more approach a practical value and are suitable for solving the site selecting problem of public service facilities in all hierarchies.