The invention discloses an experimental device of 'wet' rotor effect of a multi-stage centrifugal pump, which comprises a multi-stage wet rotor platform (9) and the like, wherein the multi-stage wet rotor platform (9) comprises a pressure-bearing shell which is internally provided with at least two stages of rotor sections, and a rotating shaft (18) passing through the pressure-bearing shell; each stage of rotor section consists of a high pressure bin (25) and a lower pressure bin (24) provided with a pump rotor (26); inter-stage seal (28) is arranged between the high pressure bin (25) and the lower pressure bin (24); the shaft neck part at the root of the pump rotor (26) is provided with a speed displacement sensor (22); a pressure circulating system is respectively communicated with the high pressure bin (25) and the lower pressure bin (24); a driving motor (3) is connected with a rotating shaft (18) by a belt pulley speed changing device (4); and a torque rotating speed measurement instrument (6) is positioned between the belt pulley speed changing device (4) and the rotating shaft (18). The experimental device can be used for measuring the amplitude and the torque of a multi-stage wet rotor along with the change of the rotating speed under the different working pressures and inter-stage seal structures.