The invention discloses a regulatory gene ZmMIKC2a for corn starch synthesis and an application of the regulatory gene ZmMIKC2a and belongs to the technical field of gene engineering. The gene has a nucleotide sequence shown in SEQ ID NO.1, the total length is 810 bp, and 269 amino acids are coded in total. Transgenic function analysis finds that the gene can increase the content of corn amylase, change the size of starch particles in grains and regulate the starch synthesis related gene expression level; the discovery of the gene provides a new basis for corn starch synthesis regulation mechanism and lays a theoretical foundation for creating superior new corn varieties, and a new way is provided for regulating and improving the balance degree of corn amylase and amylopectin with the gene engineering technology.