We have studied the aggregation of silver sol by mixing silver sol with several kinds of ions. We found that it is very difficult for the monovalent metal ions to make silver sol aggregate. The metal ions of the second main group can make silver sol aggregate and form fractal state. With the radii of metal ions increase, their ability of aggregation increases accordingly. The metal ion of the third main group A13+ can also make silver sol aggregate and form fractal state. As for acid radical ions, they can not make silver sol aggregate directly, but they can influence the speed of the aggregation and final state of silver sol. The simple explanations of these phenomena were given. We also found that the speed of aggregation and final state of silver sol were determinded by the state of silver sol and the proportion of metal ions in silver sol.