Proposed in this paper is an evaluation method of energy consumption suboptimization with chilled water pump group, and according to this evaluation method, an optimized random step optimization method is used to optimize the design of the model in pumps group. Then, the influences of control pressure difference and rated flow on annual energy consumption characteristics are analyzed by an example, and different frequency conversion control modes are compared. The results show that (1) the optimized random step optimization method performs better in coping with locally-optimal and convergent problems than traditional optimization methods do; (2) the annual total energy consumption differences caused by different load rate distribution can reach more than 50%, so the annual load distribution must be taken into account in the energy consumption evaluation of system; (3) the system of bigger bypass pressure and lower rated flow has wider low and middle energy regions, its energy consumption under different load rate limits is far away from the lowest energy consumption and the corresponding energy consumption evaluation is more tolerant; and (4) in most cases, adopting synchronous frequency conversion control becomes advantageous with the increase of flow or control bypass pressure rating.