ABSTRACT This paper solves the problem of predefined‐time stabilization for low‐order nonlinear systems with time‐varying orders and the asymmetric output constraint. We construct a tangent‐type barrier Lyapunov function to handle the output constraint. By using the presented barrier Lyapunov function and the adding a power integrator technique, a novel continuous state‐feedback controller is designed to guarantee that the solution of the closed‐loop system is predefined‐time stable while the output constraint is not transgressed.