This study is based on the Simple View of Reading, which investigated (1) the preschool predictors of high-risk children with difficulty in either character reading or reading comprehension; and (2) the discriminant and classification function of children with reading difficulty. A 2-year-longitudinal study was used to observe 273 children’s development in reading related cognitive skills and reading ability from preschool to first grade. In preschool year, reading related cognitive skills including tonal awareness, syllable deletion, phonological decoding in Tzuyin system, and Rapid Automatic Naming (RAN) as well as oral comprehension were measured; up to the first grade, children’s reading abilities in character reading and reading comprehension were assessed. The results revealed that (1) the tests developed in the first year of this study have satisfied reliability, except for syllable deletion test that reached the ceiling effect; (2) Rapid digital name is the most significant predictor of character reading in the first semester of grade 1, the second is syllable deletion. The ability of pseudo-syllable reading in Tzuyin significantly predict character reading ability in the second semester of grade 1. In addition, preschool language comprehension was the most important predictor of reading comprehension ability in grade 1; (3) RAN was the most optimal variable for classifying children with difficulty in character reading, while language comprehension was more important for classifying children with difficulty with reading comprehension; (4) early character reading ability can also be the important references for screening reading difficult children. The main contribution of the present study is to provide early predictors for screening children with reading difficulty. The results of this study also reflected the Simple View of Reading.