With the development of the forestry, useful information intelligently abstracted from mass forestry data have been widely applied. A data mining system applied in the second type of investigation in the forestry resources and the related experimental example of association rules mining for forestry are provided in this paper. The application of data mining based on related rules on the relation of property, origin, age, chest circumference, height and canopy density of trees is discussed. The Apriori algorithm has provided a reference for the decision-making support. The promising prospect of the application of the data mining system in investigation and analysis of data of the forestry resources has been proved.