Abstract: The study probed into the cognitive activity and the development of the children from 3 to 5 years of age in magnitude comparison of one-figure number. Three experiments were included. In Experiment 1, the psychological representative model in magnitudes of one-figure numbers were explored. In Experiment 2, the semantic code characteristics of the numbers and the relation between numerical magnitude comparisons and semantic code were studied. In Experiment 3 ,the cause and effect research design was used to explore the influence of semantic code on the judgment of numerical comparisons. The results showed: 1.The comparison of numerical magnitudes made by children was influenced directly by their semantic representation of numbers.2. The children presented the discrete category model gradually in magnitude representation of one-figure number as their ages increased. As a result, the process of magnitude comparison of one-figure number developed gradually from the random and disorder course to the hierarchical comparison course

Key words: children, magnitude comparisons, cognitive development, information processing