This article describes a new magnetorheological fluid damper; its damping and stiffness are variable and controllable through the compact structure of two damping units and a spring. The ability of variable stiffness and damping enables it to be used for more effective vibration control in wide-band excitation wave occasions. First, the effective stiffness and output damping force are calculated in theory. Then, the magnetic field is simulated by finite element analysis. After the prototype of the new magnetorheological fluid damper is developed and machined, the damper's performances are tested in a hydraulic actuated MTS machine, including stiffness variability and damping variability in different current. The successful development, numerical calculation, and experimental testing shows that the new damper not only outputs a controllable damping force but also occurs as the great variable stiffness in a certain range, which makes the true design and implementation of the concept of variable stiffness and damping.