This paper proposes the software package SISCON, dedicated to the evaluation of optimal decisions for large-scale systems. SISCON firstly evaluates mathematical models developed from experimental data using LS methods for linear and non-linear systems and after that computes the optimal decision problems, solving the mathematical non-linear programming problems. The large-scale systems have generally a complex structure and global approach computation cannot be carried out. The authors present a decentralised decision structure having a well-defined distribution of supervisory functions. After decomposition of large-scale problems is carried out, sub problems are solved using standard optimization techniques. SISCON offers opportunities for solving non-linear mathematical programming problems and for evaluating optimal decisions in large-scale systems control.