This paper proposes a variable stiffness and damping impedance controller with a new closed-loop impedance architecture containing the negative power type stiffness and damping parameters. The sliding mode control technique is employed to construct an asymptotically stable reduced order system using PID sliding surface. The external disturbance is well considered, which easily propagate to the preset impedance architecture to degenerate the impedance performance. To address this problem, a disturbance observer is introduced into the control system to reduce the adverse effect by partially eliminating the disturbance. The proposed impedance architecture owns better transient performance compared with the trivial spring-damper impedance architecture, which is well illustrated by numerical results.