Abstract: Influencing the assembly precision of high-precision products, the contact state of product mating surfaces is taken as a crucial factor, and a fractal-Iwan coupling model is provided usually as an effective approach to describe stick-slip contact between typical mating surfaces. In order to solve the deviation problem of the normal force calculation on small contacts with existing fractal-IWAN coupling model based on MB, caused by considering all micro-convex bodies been deformed completely and shared a constant elastic-plastic critical area globally, an improved fractal-discrete Iwan stick-slip contact mechanical model was established and a continuous scale fractal convex distribution function was proposed, obtaining a scale-dependent critical area expression. Based on the improved coupling model, the hysteretic characteristics of the rough contact interface were investigated under tangential load, obtaining the influence of contact surface geometry and contact pressure on the interface tangential force. Comparing the hysteresis curves with experimental results in the literature, the accuracy of the improved fractal-discrete Iwan coupling model was verified.