To realize the formation control of multi-robot fish system, this paper presents a new method, a position feedback control strategy, which considering both graph theory and information interaction between the robots. And a concept of reference robot fish is introduced, which means a different fish is set to stay still at any time. Other fish adjust the positions according to the position of reference fish through the information interaction, which can make the robot fish achieve any formation in the limit time. We conduct simulations on the underwater robot polo game 2D simulation platform and give out the experimental results under different situations. Simulation results show the method good integrity, good robustness and the immunity to interference, which verify the effectiveness of the proposed algorithms.