Given the very abstract and subjective feeling of pain and each individual's different extent of feeling of pain, each individual might send out different messages to medical personnel and caregivers. As children's language, cognitive, and behavioral capabilities are still under development, children's experience of pain usually has to be conveyed by caregivers to medical personnel. Some relevant studies have discovered that children can use scales of pain which suit children's cognitive development to express their subjective feeling of pain, and children consider a visualized scale of pain as the easiest scale to understand and to express their feeling. This study selected 30 children aged from 4 to 6 as research subjects, and surveyed their understanding of facial expression pictures in the Faces Scale as well as the corresponding degree of pain represented by pictures of faces in the Oucher Scale. The results suggested that children have better understanding of the different degrees of pain revealed by different facial expressions in the Oucher Scale, yet have difficulty associating the pain with their own feeling. On the other hand, it appears more difficult for children to associate the different graphic facial expressions in the Faces Scales with different feeling of pain. Nevertheless, using a crying face as an indication of pain in both scales helps children to associate the facial expression with the feeling of pain.