The purpose of this study was to inquire the influence of students' argumentation quality based on cooperation-learning instruction. The samples were 68 seventh-grade students. Experimental group used cooperative-learning instruction, and the other class used traditional instruction. The content of instruction included four issues, that is, assisted reproduction, cloning sheep, organ transplant and genetically modified organism. After four-week instruction, the study showed the differences of argumentation quality in two classes at the beginning and the end of the instruction. In order to facilitate comparison, the researchers developed a set of verification criteria to analyze the interview data and to evaluate the argumentation quality of students. The results showed that students’ argumentation quality becoming better in both experimental and control group after instruction. Additionally, the experimental group showed significantly better argumentation ability than control group. This result shows that cooperation-learning instruction has a better effect on improving student's argumentation ability than traditional instruction.