The utility model provides a flow protection controlling means is revealed to reactor coolant pump bearing seal, allow output module and main pump behaviour movable mould piece including three logic control return circuit, the logical decision module that has three -input and an output, the AND gate that has stream input and an output, signal, three logic control return circuit all includes flow transmitter, signal processing module, value judge module and the time delay module of connecting according to the preface, the three -input end of logical decision module links to each other with the time delay module that corresponds respectively, and the output links to each other with an input of AND gate, another input and the signal of AND gate allow output module to link to each other, and the output links to each other with the one end of main pump behaviour movable mould piece, the other end of main pump behaviour movable mould piece links to each other with the main pump gate. Implement the utility model discloses, can overcome protection controlling means's protection logical design's among the prior art weak link, avoid protecting the main pump mistake to move and refuse, reach the risk reduction, reduce the level of safety's of economic loss and the operation of reinforcing nuclear power purpose.