Abstract: In biomimetic interactive experiments of robotic rats and laboratory rats, the robotic rat should be very close to the laboratory rat in the respects of morphology and behaviors. In this view, the structure of our previous robotic rat is optimized to make its morphology more similar to a laboratory rat. 4 indexes, including the maximum pitch angle (MPA) and the maximum reachable height (MRH), the maximum bendable angle (MBA) and the minimum bendable distance (MBD), are proposed to assess action primaries of the robotic rat including the pitch and yaw motions. Experiments show that the optimized robotic rat has good performance of pitch motion and its yaw motion needs to be further improved. Then, the model of motion similarity between the robotic rat and the laboratory rat is established with 2 quantization parameters. One is the first key impact factor based on the pitch and bend angles, and the other one is the second key impact factor based on the arrival height and bendable distance. The 2 key impact factors are calculated by simulating 3 typical behaviors of a laboratory rat, and the similarities of the 3 behaviors are then obtained to be 96.12%, 98.68% and 96.61%, respectively. The results demonstrate that the robotic rat can achieve high-quality action simulation of a laboratory rat.