Abstract: Based on Moody chart and Look-White equation, sieves a complete package of calculating formulae about frictional resistance coefficient of single-phase fluid along each flowing region inside circular pipe from a number of relational expression and distinguishing limit between each region. According to single-phase fluid's frictional resistance coefficient and Reynolds number Re, the relationship of relative roughness is divided into five flow pattern regions: laminar region, transition region between laminar flow and turbulent flow, turbulent flow smoothing region, turbulent flow mixing frictional region and turbulent flow roughness region. The other regions exist recommended equations except the transition region between laminar flow and turbulent flow which has not been fully recognized at present due to a small range and complicated flow.