Abstract: The Boundary Element Method (BEM), as a key numerical method, has been widely applied in many fields. However, the research on the Direct Boundary Element Method (DBEM) for ship hydrodynamic numerical calculation problems is still insufficient, especially when it comes to the ship hydrodynamic potential flow theory. The general method-‘panel method’-is based on Hess-Smith method, which is an Indirect Boundary Element Method (IBEM) whose major flaws exist in both theory and numerical calculation. This paper, based on the ship hydrodynamic potential flow theory, adopts DBEM to calculate the example of two-dimensional unbounded potential flow around a cylinder, and analyzes the influence of the boundary element discrete forms and the numerical integral methods on the calculation accuracy. The results carried out by Matlab clearly indicate that using the constant element and Romberg algorithm method could yield high calculation speed and accuracy.