Because of its enormous applications in fluid engineering the study of flow through a curved duct is of fundamental interest currently. Here, it is an elementary effort on studying the Isothermal fluid flow through a curved duct with square cross-section under various flow conditions to identify the detail flow behaviors. The numerical technique Spectral method is used as a main tool for solving the mathematical model, where the secondary tools are Chebyshev polynomial, the Collocation methods and the Newton-Raphson method. Results are also shown in graphical form.