Experimental studies are conducted for the wave forces acting on the vertically mounted circular piles in the waves. Two-three-cylinder arrays are equally spaced and the spacings(S/D) as well as the incident angles of various waves are changed to study their separate effects on the wave forces. The numerical results based on the diffraction theory are in good agreement with the experimental results, and the diffraction theory well predicts the trend of the wave forces when the spacings and the incident angles are changed.