The role of the semantic radical is important to understand the cognitive mechanisms of lexical processing. However, it is still unclear about the cognitive accounts of developmental changes of the semantic radical on lexical processing, including the sublexical and the neighborhood size account. In the present study, we address this issue by recruiting 60 third graders, 54 sixth graders and 28 college students. Participants were tested using the lexical decision task. They had to decide whether a visual symbol was a real Chinese character. Frequency (high, low) and radical combinability (high, low) were independently varied to study lexical processing. There were two main results. First, a significant frequency effect was found across three age groups during the lexical decision task, suggesting that lexical access was involved in the task for participants. Second, for the third graders there was a significant effect on radical combinability effect, with better sensitivity performance on characters with high combinability. This finding suggests that third graders may rely more on the knowledge of the sub-lexical component (i.e., semantic radical) within a character to facilitate their lexical decision judgments. This result can be explained by the bi-directional activation model, using the interactive activation of sublexical and lexical information during lexical processing. In contrast, there was no significant effect on radical combinability in both the sixth graders and college students. We will present several views and future directions to explain the differences in radical processing between children and adults.