1. It achieves automatic cap screwing function with three pairs of friction wheels. To prevent damaging bottle caps due to excessive torque forces on the rear two pairs of friction wheels, friction clutches are installed on the said wheels, realizing automatic slipping due to overloaded torque so as not to damage bottle cap surface. 2. Inverter stepless speed regulation is adopted for cap screwing at various speed levels. Such adjustment is reliable and stable. 3. There are two conveying closure forms: lifting conveying form; oscillating conveying form. 4. There is a special cap flipping and return flow device in the lifting conveying form, which ensures no flipping defect during conveying. 5. The same set of cap screwing machine can be adaptable to cap screwing functions of various bottles.