For investigating on the surface morphology variation of structure ceramic materials and its effect on the friction characteristics during friction, the relationships between contact and mechanical were analyzed in friction process. Meanwhile, the friction characteristics of Si3N4 ceramic samples machined by rotary ultrasonic grinding, such as friction surface morphology and friction coefficient were studied with experiments. First, according to the contact characteristics and material properties, the calculation formula of the total load was deduced based on fractal theory. The friction coefficient fractal model was also established on the basis of above. The analysis results shows that the relationship between friction coefficient and surface profile fractal dimension after friction is similar to the normal distribution curve, when the initial surface profile fractal dimension is 1.4, 1 45, 1.5 and 1.55 respectively. Then with surface to surface contact friction experiments of Si3N4 ceramic sample machined by rotary ultrasonic grinding, surface topography and friction coefficient variation after friction were investigated. And the influence factors on the friction coefficient were also analyzed. The results indicate that micro-cracks are the notable feature of the surface morphology for Si3N4 ceramic friction. The temperature of 160℃ is the inflection points of fall and rise for Si3N4 ceramic friction coefficient. The friction coefficient is the maximum when the applied load is 360 N and reciprocating frequency is 80 Hz. It concludes that the machining surface morphology control improves the wear resistance of structure ceramics.