Cavitation is a challenging flow abnormality that leads to undesirable effects on the hydraulic behaviour of centrifugal pumps. This study analyses the cavitating flow at a normal flow rate using the shear stress transport k-ω turbulence model and the Zwart cavitation model to capture the cavitation development and spatial distribution of vapour structures within the pump. A general description of the pump head-drop phenomenon was analysed through the study of local and global flow fields. The relationship between vapour distribution and entropy generation fields was mainly investigated through the local flow analysis method. Results show that the tendency of total entropy generation rate within the impeller coincides with the pump head-drop curve. The entropy generation rate changes slightly at the early stage of the cavitation development whereas rapidly increases when the cavitation has fully developed. Cavitation development enhances the hydraulic losses and flow unsteadiness in the impeller. These hydraulic losses are located substantially at the interface of the cavity, especially at the rear portion of the cavity region.