In the present study, a novel testing system is presented for obtaining distribution characteristics of pressure field inside a low specific-speed centrifugal pump with atypical open impeller, wherein the components of the system are described in detail. At three rotational speeds, the instantaneous static pressure on the casing wall of blade tip clearance and volute wall are measured under different flow conditions. The average static pressure fields are obtained and standard deviations of the pressure are also determined. The results show that the pressure distribution characteristics on the casing wall can vary with the location observed and working condition operated, and the pressure pulsation amplitude is more severe than that on the volute wall. The pressure pulsation is always the most dominant under the shut-off condition. Due to wall roughness and blade tip clearance leakage, the static pressures at the same radius circle demonstrate unsteady characteristics. From the second to the sixth cross-section of volute, the average static pressures are nearly constant as a whole, but after the sixth cross-section, the average static pressure distributions depend on the working condition significantly.