Under the effects of rapid changes in current social environment and family, family structure gradually changes from past extended family and stem family to nuclear family for matching modern social environment. Preschool children’s learning is affected by school education as well as family education. When different family socioeconomic status would affect children’s cognitive ability to form the stratification of cognitive ability development, such a phenomenon is growing apart from the philosophy of equality of educational opportunity. Aiming at parents of children in preschool education units in china, as the research objects, total 360 copies of questionnaire are distributed, and 237 valid copies are retrieved, with the retrieval rate 66%. The research results are summarized as below. 1. Children with higher family socioeconomic status present better cognitive ability, explaining the actual effect of family socioeconomic status on current children’s cognitive ability to form educational stratification as well as unequal opportunity for preschool education. 2. The higher family socioeconomic status shows the richer family educational resources. It is therefore inferred that children with higher family socioeconomic status reveal better cognitive ability, possibly because of richer family educational resources allowing children receiving more cultural, social, or financial capital stimulation to enhance more cognitive ability. According to the result to proposed suggestions, it is expected to enhance domestic ideal of equality of preschool educational opportunity, allow domestic education parallel to various advanced countries, and achieve the responsibility for cultivating quality citizen in the future.