Mean decision power(MDP)is an important criterion of a new reduction model,and relative decision power(RDP) and amount of rules(AR)are key parameters of MDP.This paper presents two important properties:relationship between RDP and AR,and relationship between MDP rule set of parent decision table and MDP rule set of child decision table.These properties can help better understanding of the new reduction model and are useful tools by which one can rapidly derive an MDP rule set. Mean decision power (MDP) is an important criterion of a new reduction model, and relative decision power (RDP) and amount of rules (AR) are key parameters of MDP.This paper presents two important properties: relationship between RDP and AR, and relationship between MDP rule set of parent decision table and MDP rule set of child decision table. These properties can help better understanding of the new reduction model and are useful tools by which one can rapidly derive an MDP rule set.