With respect to the collaring jam problem found when harvesting intact rice straw by using domestic small and medium-sized steel-roll round balers, the baling mechanism, which combines the side disk and steel rolls (“the roll-disk type” for short) was designed, and the baling process was experimented by the roll-disk round baler. Through high-speed photography and kinematic analysis, it was found that after being fed to the baling chamber, the intact rice straw can move circumferentially along the steel rolls of baling chamber under the combined effects of steel rolls and side disk;when the rice straw returned to the bottom of baling chamber after running a cycle in the baling chamber, the rice straw would stop rotating due to friction force on two side walls of the baling chamber, then it was continuously accumulated at the bottom of baling chamber;the friction driving force generated by side disk on rice straw can shorten the process of rice straw accumulation to form rotating straw core, which can prevent collaring jam. Based on this, the main factors that affected the formation of rotating straw core in the roll-disk round baler—disk diameter, disk rotation speed and lengthwidth ratio (ratio of rice straw length to width of baling chamber) are chosen as the experimental factors, the rice straw mass when forming rotating straw core was decided as the evaluation index, and then experiments were conducted. The experimental results showed that the sequence of various factors’ influence on the evaluation index was disk diameter, length-width ratio and disk rotation speed. When the disk diameter was 380mm, disk rotation speed was 135r/min, length-width ratio was 1.00, rice straw mass when forming rotating straw core was 1.21kg, and the length-width ratio was 1.26, the rice straw mass when forming rotating straw core was 3.44kg, and there was no jam occurred. The research results can provide theoretical and technical basis for design of roll-disk round balers and optimization of its operating parameters.