Granular computing aims to provide different views at different granules of data, and to derive knowledge from the process of data abstraction. In this paper, a decision-rule generation algorithm based on granular computing (DGAGC) is proposed. The DGAGC consists of two stages, the rule generation stage and the decision making stage. In the rule generation stage, the DGAGC employs a rule combination strategy and an alternative rule generation strategy to increase the accuracy of rules and the speed of generating rule in higher granularity. In the decision making stage, the DGAGC provides a novel rule-choosing strategy to use reasonable rules for decision making. By using this rule-choosing strategy, a better decision is made from many reasonable rules which are generated in stage one. The experimental results show that our algorithm works better than a prior similar study.