There are more or less confined particles in mechanical frictional interface. These particles, asperities contact, and local fluid lubricant constitute the mix-friction state with obvious frictional nonlinearity together. This paper first illustrates the embodiment of frictional non-linearity in mechanical frictional pairs and the mechanism of confined particles in this problem, and the different effects of confined particles in mechanical pairs including reducing friction, increasing friction, inducing noise, and the inducing of the instability of friction force are briefed. Focusing on the frictional instability induced by the confined particles in mixed-friction, this paper concludes different experimental studies of the frictional interface with confined particles under different application backgrounds including the particular couette flow experiment, the SEM observation of powder layer, the experiment research about intruding particles and wear particles, then, the blank and difficulty of the experimental research about the confined particles in mechanical frictional pairs are summarized. The advantages and disadvantages of different modeling methods are analyzed and the trend about the modeling research of the behavior of confined particles in frictional interface of future modeling job are proposed. Finally, the mechanisms of stick-slip and creep phenomena induced by confined particles are analyzed, and the research significance is illustrated.