Abstract: This paper assumes that the oil-flow in the clearance is steady axial symmetric laminarflow of viscous incompressible fluid and axial vilocity Vz=0, and a calculation formula for carrying-capacity of annular hydrostatic step-bearing taking account of oil-flow inertia is obtained by means of Navier-Stokes' equation of motion. This calculation formula for carrying capacify of round hydrostatic step-bearing is given with the aid of present formula directly.These formulas not only the engineering applications are useful, but also regard as the theoretical basis for analysis of working character of hydrostatic step-bearing.