Plant surface waxes form an outer barrier that protects the plant from many forms of environmental stress. The deposition of cuticular waxes on the plant surface is regulated by external environmental changes, including light and dark cycles. However, the underlying molecular mechanisms controlling light regulation of wax production is are still poorly understood, especially at the post-transcriptional level. In this paper, we report the regulation of cuticular wax production by the miR156-SPL9 module in Arabidopsis. Compared with wild-type plants, miR156 and SPL9 mutants showed significantly altered cuticular wax amounts in both stems and leaves. Furthermore, it was found that SPL9 positively regulates gene expression of the alkane-forming enzyme CER1, as well as the primary (1-) alcohol-forming enzyme CER4, to enhance alkane and 1-alcohol synthesis respectively. More importantly, our results indicate that complex formation of SPL9 with a negative regulator of wax synthesis, DEWAX, will hamper SPL9 DNA binding ability, possibly by interfering with SPL9 homodimerization. Combined with their diurnal gene and protein expressions, this dynamic repression-activation transcriptional module defines a dynamic mechanism that may allow plants to optimize wax synthesis during daily cycles. These findings provide a regulatory framework for environmental signal integration in the regulation of wax synthesis.