Abstract: On the basis of analysing and studying systematically theforces acting on balls and inner rings(or outer rings)of high speedradial ball bearings in rocket gyroscopes(are called“high-speed ballbearings”for short)by means of the rolling bearing theory,the rollingtheory in tribology and the principles in elasticity mechanics,a group of formulas for calculating friction coefficients of high-speed ball bea-rings has been advanced in this paper.The analytical relationshipsexpressed by the formulas derived indicate clearly that the frictioncoefficient of a high speed ball bearing is related to not only the bore,outer diameter,sliding friction coefficient between ball and inner ring(or outer ring),ball diameter,ball number,but also the rotativespeed and equivalent dynamical load of the high speed ball bearing.