The paper introduced the composition and working principle of new stretching mechanism of iron roughneck for “crust Ⅰ” myriameter drilling rig, made theoretical calculation on the velocity of the parallelogram mechanism used and conducted dynamic simulation analysis by ADAMS software. With different load and drive modes on the stretching cylinders, the dynamics process of stretching mechanism was investigated. The results indicate that the design of stretching mechanism is reasonable, smooth and reliable.