At present, traditional data-driven nonlinear system modeling methods primarily focus on model fitting and application. In this context, this paper constructs an upper boundary model based on least squares support vector regression (LSSVR) for the maximum tolerable output of a critical parameter from the system, which is influenced by uncertainty. The study delves into the relationship between the balance of model accuracy and sparsity, and its effect on the model output. First, by utilizing the optimization problem of LSSVR, the original equality linear constraints are transformed into inequality constraints that satisfy the upper boundary model. Next, to improve the model’s accuracy, an inequality constraint based on the approximation error between the predicted output of the upper bound model and the actual output is introduced. Meanwhile, the LSSVR’s weight L₂-norm is employed to control the complexity of the upper boundary model’s structure, thereby constructing a new objective function and establishing a new optimization problem that satisfies the inequality constraints of the upper bound model. Finally, the Lagrangian function is introduced into the optimization problem, and the Karush-Kuhn-Tucker conditions are used to derive the corresponding dual optimization problem, which is then converted into a standard quadratic programming problem to solve for the parameters of the upper bound model. Since the new optimization problem satisfies convexity, the solution for the model coefficients is globally optimal. The effectiveness and superiority of the proposed method are validated through experimental analysis, where the maximum approximation error, root mean square error, and sparsity-related metrics are used to reflect the model’s accuracy and sparsity characteristics.