A connecting assembly for an electric cylinder and a control box includes an electric cylinder, an electric control box and a sheathing ring. The electric cylinder includes an actuator and a contractible pipe module perpendicularly connected to an end of the actuator. The electric control box is disposed on an internal side at a right-angled position with respect to the actuator and the contractible pipe module and slidably connected to a side of the actuator. The sheathing ring is sheathed onto a contractible pipe module and slidably connected to a side of the electric control box. The connecting assembly of the invention not only achieves a screwless application, but also provides a quick, simple, convenient and stable assembling process.