The electric submersible pump (ESP) is a centrifugal pump with several stages. It's a dependable and efficient industrial lifting tool for lifting different amounts of fluids, and it's known for its adaptability and reliability. Electric submersible pumps are commonly used in onshore oil wells, as well as underground pumping and other applications. The pump's efficiency is evaluated under the control of various rotational speeds. The CFD approach is used in this analysis to analyze flow behaviors within the ESP at various flow speeds. ANSYS CFX program was approved to conduct and investigate single-stage simulation of the GN7000 pump. The sensitivity of the network was determined, and the best mesh for the solution was chosen. The flow field was solved using the (SST, Unsteady-RANS) model with different rotational velocities (2500-3000-3500 cycle in this case). The test used two fluids with varying viscosities, and the findings revealed that the viscosity has an impact on efficiency as well. There is a high level of compatibility as compared to previous studies. This research presented a set of curves for efficiency and pressure and to know the extent of the effect of rotational speed on performance in general