  The properties of pairing correlation in nuclear matter are investigated by
using various versions of Skyrme forces. Truncation of states involving pairing
correlation, necessary due to zero range nature of the Skyrme force, is
discussed in detail. A plateau appears in pairing gap versus cutoff for each
force. We propose to choose the cutoff parameter in the middle of the plateau
so that the parameterization is independent of nuclides.
