A knowledge-based variable-structure decoupling is developed, and be utilized to control a nonlinear multivariable system, so as to avoid the model-establishing process, especially avoid large amount of complex matrix operations required for the conventional decoupling control. Some modules in the knowledge base of this kind of control are described, and the main points of the related algorithms are introduced. Strategies described in this paper have been successively utilized to the set-point temperature control of a 3 × 3 strong coupled system —a three winding heater type standard temperature source, and an effect that the temperature stability as well as temperature homogeneity all better than 1℃ has been attained, which is impossible for the conventional control method.