This article proposes a novel tunable predefined-time nonsingular sliding mode control (SMC). Based on the definition of tunable predefined-time stability (PTS), a new inequality condition is proposed to ensure the tunable PTS of the system and provides a detailed proof. Based on the proposed lemma, this article combines tunable PTS with SMC, which not only ensures the robustness of the system but also accurately estimates the boundary value of convergence time (CT), which is independent of controller parameters and initial states, and the actual CT is adjustable. In addition, this article solves the singularity problem of a traditional SMC. Finally, the effectiveness of the proposed method is verified by both simulation and physical experiments.