276 research subjects from Primary 1 to Primary 6 were invited to write in Chinese. 828 written samples were collected. Whole language approach was used in teaching writing. Students can write without too much guidance and can express their own idea freely. Researchers tried to find out the total number of Chinese characters and words, the number of types of characters and words, and the type-token ratio of words of the samples in different grade levels. The developmental characteristics were also investigated. The research findings were compared with similar studies in China and Taiwan district. It is found that there was correlation between the language performance, writing performance and the number of vocabulary used by the research subjects. Researchers also examined the developmental characteristics of errors of vocabulary. Research results indicated that the present teaching materials for vocabulary learning are not effective. Pupils have learnt vocabulary, which they do not have experienced. On the hand, they do not have the vocabulary to express themselves. There is a need to bridge the gap. The findings are useful for curriculum development and teaching.