This paper presents a new variable stiffness actuator based on a second-order lever mechanism which has wide stiffness regulation range. By employing a novel symmetric structure design and improving the load capacity of the stiffness regulation module, the proposed actuator also shows well performance in load capacity, stiffness regulation response, and elastic hysteresis. On this basis, a variable stiffness actuated manipulator is developed. The experimental results demonstrate that the presented manipulator possesses abilities in fast stiffness tracking, shock-absorbing and explosive movement. It is also verified that the manipulator can withstand accidental impact, which illustrates the structure stability of the proposed design.