Abstract— Study of improving the reliability and lifetime of bladed pumps is now of great importance. In this context, the key objective is to reduce the hydrodynamic vibration of screw-centrifugal pumps caused by pressure pulsations in the pump outlet casing. Due to the flow stepwise nonuniformity at the impeller outlet, pressure pulsations emerge at the rotor blades passing frequency and its harmonics. These vibrations cause a dynamic load on the components of pump body causing its vibration, so the calculation of the pressure pulsations amplitude in the screw-centrifugal pump at the early stage of the design is a relevant task. When defining pressure pulsations generated by the three-dimensional vortex flow of the screw-centrifugal pump their dual nature should be considered. The heterogeneous distribution of the flow parameters at the outlet of the centrifugal impeller generates acoustic disturbances that are propagated at the speed of sound in the operating fluid. At the same time, there are vortex disturbances that are convected by the main flow. Vortex oscillations of the main flow parameters is called "pseudosound" or the vortex mode. This paper develops a three-dimensional acoustic-vortex method of calculating pressure pulsation, which provides the ability to determine the amplitude of acoustic mode. It shows the derivation of the acoustic and vortex equations and the calculation example of the pressure pulsations amplitude at the screw-centrifugal pump outlet with different guide channel design. It shows the ability of modeling the combination components in the spectrum of pressure pulsations.