With strong adaptability to complex terrain, quadruped robots have been widely applied in real-world tasks. To enhance quadruped robots’ environmental adaptability in narrow space, one solution is to design a small-sized biomimetic robot that has multiple locomotion and posture, such as the rat robot. There is a great challenge to design a small-sized biomimetic robot with high velocity and high flexibility. To do this, inspired by mice in nature, the rat robot is designed with a soft actuated spine, which can do lateral flexing and optimize legs locomotion.