The flow field around a rectangular cylinder with an aspect ratio of 4 was simulated with Reynolds-averaged Navier-Stokes equations combined with SST k-ω turbulent models, which helped to represent its flow structures and aerodynamic characteristics. The results obtained, including drag coefficient, Strouhal number, mean and fluctuating pressure distribution on cylinder surfaces, averaged vortex shedding location and reattachment length, agreed well with available reports. Through the application of the Principle Component Analysis (PCA) to records of fluctuating pressure on the surfaces, it is found that the first principle component shares the same trends with the RMS distribution of fluctuating pressure, which may be an alternative way to characterize the fluctuating pressure. Based on the configuration of the first principle component, the vortex shedding location on the side surface can be readily located, and the vortex shedding frequency can also be obtained from the coefficients of the first principle. It is highlighted that the main vortex shedding on the side surfaces dominates the features of the fluctuating pressure.