Abstract: For rotating machines or rotational energy harvesters, keeping a constant rotating shaft speed is the key to maintain the stability of energy transfer and prevent component damage caused by sudden loading. In this study, the shear thickened non-Newtonian fluid is designed to inject into the clearance between the shaft and the shaft sleeve. The adjusting effect of the non-Newtonian fluid on the rotating speed of the shaft is studied by theoretical analysis and numerical simulation. The effects of the parameters viscosity, consistency coefficient, rheological index, yield stress etc. on shaft speed were investigated for non-Newtonian fluids including Bingham fluid, power law fluid, Herschel-Bulkley fluid and Sisko fluid. It is found that under a certain external load, the shear thickened non-Newtonian fluids have a fast adjusting effect on the rotating speed of shafts.