The article considers synthesis of an expert system for controlling electric power consumption by pumps of main water drainage facilities of an underground mine on the basis of the Mamdani fuzzy inference algorithm. The proposed system has a MISO-structure (multiple-input, single-output) with two input variables, such as water inflow and power cost as well as one output coordinate – power of pumping units. Two bases of fuzzy rules such as conjunction (AND) and disjunction (OR) are formed. By simulation modelling, a comparative analysis of fuzzy control systems for power consumption by water drainage facilities is carried out, as well as a system without control, when the pump performance is stabilized, during week and month periods. It is established that OR-rule based systems can reduce power costs by 1.89% during a week and by 2.28% during a month, and AND-rule based systems by 4.13%, as well as by 5.43% during week and month, respectively. At the same time, we note that the economic effect is achieved not through a decrease in power consumption, but by adjusting the operation mode of the water drainage facility, which involves ensuring maximum efficiency of groundwater drainage when the power cost is high, and minimum efficiency when it is low.