Cyanobacteria are the simplest organisms to have circadian clocks.The central oscillator in cyanobacteria is com-posed by a transcriptional/translational feedback loop(TTFL)and a post-translational oscillator(PTO).The PTO is a core pacemaker which consists of three proteins KaiA,KaiB and KaiC.KaiA stimulates the phosphorylation of KaiC,while KaiB inhibits the activity of KaiA.The cyanobacterial circadian clock is an interesting topic for researchers and many mathematical models have been constructed.However,the current mathematical models of the cyanobacterial circadian clock have been made only considering the interactions between Kai proteins.CikA,as an input pathway component,plays an essential role in the circadian clock,whose mutation results in abnormal rhythms.The regulation mechanism of CikA remains unclear.In this paper,we develop a detailed mathematical model for the cyanobacterial circadian clock with incorporation CikA-regulation.Based on numerical simulations,we explore the dynamic properties of the circadian clock regulated by CikA.The results show that the regulation of CikA makes the system more sensitive.In detail,CikA strengthens the central role of PTO and improves the adaptability of the circadian clock against the change of environment.With CikA,the system is able to modulate its period more easily to face environmental perturbation.CikA also enhances slightly the fitness of cyanobacteria.The findings of this paper can supplement the biological research and may help us more clearly understand the cyanobacterial circadian clock regulated by other proteins.