This paper anatomizes all actions in planning domain, proposes a descriptive method for the relations between preconditions and effects of action, and defines some basic relations between preconditions and effects of action, such as direct concomitant relation, conditional concomitant relation, and direct obstructive relation. These basic relations express the domain knowledge hiding in the definition of actions. For these basic relations, this paper defines some compound operations, and obtains indirect obstructive relations and absolute obstructive relations. The indirect obstructive relation shows the transitivity of preconditions of action, and the absolute obstructive relation expresses the impact on other predications when one predication is realized by action. Finally, this paper gives some applications of these relations in the planning system. These relations are the essential theory basis for sorting predications in target state, judging the target state, and optimizing the strategy of action selection for one predication.