A new coordination number model for square-well (SW) fluid is proposed in this work. It is based on the local composition theory and starts from the point that total site numbers around one molecule can vary with reduced density and reduced temperature. The total site numbers are correlated with reduced density and reduced temperature by using local composition theory and Monte Carlo (MC) simulation results. This new model agrees well with the MC simulation results for the pure SW fluids at the low-density limit and in the high-density region. In addition, it can predict the transition to the face-centered cubic (fcc) fluid property which is shown in Young and Alder's [J. Chem. Phys. 73 (1980) 2430] phase diagram. An equation of state (EOS) is derived from this new coordination number model and gives satisfactory compressibility factors for SW fluids.