Abstract: Experimental investigation into frictional contact forces is key works on friction induced vibration and noise. In this paper, a test bench based on a pin-on-disc system was established and frictional squeal was successfully reproduced. The three direction contact forces were sampled by using a three-dimensional force transducer under squealing and non-squealing conditions. The measured signals were analyzed through wavelet decomposition, statistical probability, power spectral density and time-frequency analysis methods. It is found that the friction force and normal force had high-frequency pulsation during system squealing, and they were the excitation source of squeal. The dynamic part of friction force and normal force under non-squealing conditions were typical white-noise signals which were non-Gaussian distribution. The dynamic part of friction force was either non-Gaussian distribution, while the normal force was close to Gaussian distribution. Mode coupling mechanism was the origin of high-frequency frictional squeal and high-frequency oscillations of frictional contact forces.