This study aimed to investigate the generation mechanism of pairwise associated sketches and different associated types through the experimental analysis of the cognitive processes of the designers in conceptual design process. The verbal protocol analysis (VPA) was carried out on three groups of participants (designers). The first group consisted of eight university students majoring in industrial design, the second consisted of eight university students majoring in mechanical design, and the third consisted of six product designers with degrees in industrial design and over 5 years of work experience. Their cognitive processes revealed by the think-aloud protocol and outcome sketches during a specific design task were recorded. Following a content-oriented encoding scheme, the verbal data were encoded into cognitive actions, and according to the generation sequence of the sketches, the encoding results were postprocessed for the further analysis of associated sketches. First, we identified which cognitive actions played important roles in the generation of associated sketches. Next, based on the encoding results and the analyses of all associated sketches, we found that all associations can be categorized into three types (in order from low to high association levels): shape association, behavior association, and function association. Finally, we found that the differences in major background had no significant effect on the number of associated sketches but did have some influence on the diversity of association types, the differences in experience background mainly influenced the number of associated sketches in each type of association. Meanwhile, by analyzing the key cognitive actions, we also found the advantages and disadvantages of each group in the generation of different types of associations. The findings of this study can help designers with different backgrounds to choose suitable strategies to stimulate the important actions at the right time, conceive appropriate association types, and ultimately generate diverse concept sketches with high quality.