Abstract: By employing the knowledge(R-element equivalence class) in one direction S- rough sets and dual of one direction S-rough sets, the concept of knowledge law is given; the generation theorem of knowledge law, the excursion theorem of knowledge law, and the attribute disturbance discernible theorem of knowledge law are proposed. Knowledge law is a new characteristic of S-rough sets.

Key words: knowledge law, attribute disturbance, the balance theorem of law, the excursion
theorem of law, the discernible theorem of law