A method for calculating the hydrodynamic pressure distribution over a two dimensional body oscillating in waves using Ursell-Tasai type velocity potentials and stream functions is discussed. By modifying some points of Ursell-Tasai's method, it becomes easier to calculate the total pressure including the both radiation and diffraction pressure. The problem was solved by a method using the normal derivative of the velocity potential. The result was compared with the solution by the stream function, and it was shown that both results were the same within a negligible small difference. The convergence of the Ursell-Tasai type velocity potentials were also examined numerically. And it was concluded that for Lewis-form cylinders applied in this report the convergence was sure. As an example, some calculated results on the pressure distribution, hydrodynamic forces and wave exciting forces on oscillating or restrained bodies were shown.