Abstract: The amplitude and frequency of the exciting force are main factors which impact on performance of the lateral vibrating friction-reducing tools. Through measuring friction under the load of rotary exciting force with the self-developed testing unit, the impact of amplitude and frequency of the exciting force on the friction coefficient of plane friction pairs between steel and rock plate was diagnosed. The results show that friction coefficients reduced by 21.6%, 29.0% and 34.4% respectively when the exciting force increased from zero to 34.2 N at the frequency of 5, 10 and 20 Hz, and by 22.8%, 27.4% and 39.0% respectively, when the exciting frequency increased from zero to 30 Hz at the exciting force of 11.4, 22.8 and 34.2 N respectively. The study indicates that the friction coefficient of plane friction pairs between steel and rock plate has a negative linear relationship with the amplitude of the exciting force at the same exciting frequency, and a negative logarithmic relationship with the exciting frequency at the same exciting force.