This research aims to explore strategies which used for promoting the cognitive ability of size for developmentally delayed children. In order to complete the aim, this research employed one sample, and adopted action research. And the conclusions are as follows: Exerting the game of bear's baby in line can quickly guide sample into study situation, promoting the concept of size by children's song, enhancing the cognitive ability of size by the jumping game of bear's baby, and consolidating it by the game of classifying and pairing. Basing on conclusions, this research offers five suggestions: 1. Let child have personally operate chance, as enhance his memory and cognitive ability。2. Using finger ballad as the mean to attract his attention. 3. Parent should take them as example for imitation.4. Can adopt the game of listening and selecting to cultivate the attitude of waiting. 5. Can adopt multiple interactive role.