The reactor coolant pump (RCP) is an important equipment for transporting coolant. Its safe and dependable functioning is linked to the nuclear power plant’s stable operation. Two input conditions of the nuclear main pump were investigated in the experiment: The nuclear main pump’s inlet was connected to the straight pipe section, and the steam generator’s inlet was connected to the steam generator. The second connection mode look more like real nuclear power facilities. Due to the varied upper inlet connection, pressure pulsation with various characteristics occurs in the core main pump. When the steam generator is linked to the nuclear main pump’s input, the nuclear main pump’s pressure pulsation increases dramatically. And the entire pump has an obvious low frequency of about 3.9Hz, which has become the first primary frequency of pressure pulsation in the entire pump.